14 Steps for Email Warm Up (Before Sending Cold Emails)

You’ve probably noticed (as we certainly have) that achieving high open and reply rates has become much more complicated. Enter: Intelligent email warm up process.

When open rates consistently fall below 50 percent, reps and marketers often wonder if it's just due to subject lines—or are other factors at play? For example, emails can land in spam, where prospects don’t even have the chance to open them.

This issue of emails being automatically filtered has led top email marketers to implement a new strategy called email warm-up.

Forty-five percent of global email traffic is categorized as spam. The rise of promotion, social, and updates folders means it's never been harder to reach a prospect's main inbox because your message can be filtered and hidden in so many ways.

Since major filtering algorithm updates, email providers now look at the general engagement on your domain to create a "sender reputation," which is similar to a credit score for your email domain. Mailbox providers (like Google and Microsoft) use this sender reputation score to decide how often your emails are sent to promotion and update folders compared to the primary inbox.

Email warm-up is the best strategy for maximizing email engagement and improving deliverability. We’ll show you exactly how this works in 14 steps that you can implement in your cold email process.

How Does Email Warm Up Work?

The process involves steadily increasing your sending volume in a controlled and deliberate manner while ensuring your domain receives ‘positive interactions’ from other real mailboxes daily.

Positive interactions tell email providers that people want to engage with your content. These include actions such as replies, emails being marked as important, and emails in the spam inbox getting moved into the primary inbox.

It can be difficult to receive these positive interactions daily if you send outbound emails. Still, the good news is that following the steps we outline and turning on your email warm-up tool will help increase these interactions and help you establish a good sender reputation.

Are you looking to revolutionize your sales email strategy? Start by understanding the significance of technical email setup in maximizing your efforts.

1. Throttle Sending Over the First 30-60 Days of Outreach

Simply put, lazy marketers lose nowadays. One of the most common mistakes in cold email campaigns is picking a fixed number of cold emails to run per day and sending that volume immediately. For example, setting up a daily limit of 150 emails per user per day, adding a few thousand contacts to your campaign, and setting it to run immediately.

This spike in sending volume is an obvious spam trigger for email providers. Your emails will likely land in spam folders, and your mailboxes can be suspended.

To avoid these issues, plan your daily sending limits so your sending volume increases naturally and steadily. We call this step "throttling email sending."

Follow these rules for your daily prospecting limits during the throttling period:

1. The day-on-day increase in email volume for a single inbox can not be higher than 100 percent.
2. A mailbox's sending volume should gradually increase randomly, not by a set percentage each day. (This helps your throttling look more natural.)

Does this leave you with a math and planning problem for the campaign rollout? No! We’ve created a sheet below that automatically suggests how to throttle sending on each day your campaign is running.

Simply download the sheet right here by clicking "File>Download" (as an Excel file), enter the target number of daily emails you want to send in the "Daily Email Target" cell, and your Fast, Medium, or Slow Throttle will be calculated.

Fast Throttling is best when a new employee's mailbox is added to an existing domain/subdomain. (If your domain has a strong track record of sending marketing emails with high engagement.)

Medium Throttling is best when starting a new outreach campaign on an existing email domain with a track record of sending marketing and general business emails.

Slow Throttling: is best for starting cold outreach for the first time or on a new domain/subdomain with a limited track record of email activity.

2. Turn on Your Email Warm Up Tool

Using an email warm-up tool automatically increases the positive engagement your email domain receives. Warm-up tools do this by simulating replies and various other positive interactions (like your emails being marked as important or moved out of spam).

It’s important to understand that warm-up tools send emails and conduct positive interactions among the mailboxes in their network (i.e., other users of the warm-up tool), not your prospects' inboxes. Because email providers create their sender reputation scores based on the general engagement a domain receives, these actions inside the warm-up community help to improve your inbox placement on average.

Allegrow is an example of a warm-up tool used by everyone from start-ups to publicly traded companies to improve their sender reputation. But, of course, we’re a little biased, so if you want to get the lowdown on what makes a good warming tool, we’ll cover that a bit later.

Using warm-up tools to augment your domain's positive engagement while conducting cold outreach has become the (not so-secret) strategy businesses use to keep high open and reply rates.

It’s important to remember that even though warm-up vendors help stop your emails from landing in spam, they are not a shortcut to email marketing success. To generate great engagement through cold email, you must ensure your entire strategy follows best practices. That’s why there are 14 steps to warm up your email, not just one!

Consider these free assessment questions if you’re unsure whether you're ready for a warm-up tool.

3. Authenticate Your Emails with DKIM, SPF, and DMARC

Messages from some email domains are perceived as riskier than others based on whether the established protocols of DKIM, SPF, and DMARC have fully authenticated them.

These protocols are like having a driver's license to send emails to recipients. They are frameworks email providers use to validate that an email is coming from the expected location.

Therefore, having all three protocols in place is essential before sending any prospecting emails. To test if these protocols are set up on your Google Workspace inbox for free, enter your domain here. Hopefully, you’ll see these results, which show no issues with these protocols:

If you’re using an Outlook inbox, you can test DMARC, SPF, and DKIM records with a different provider here. (or, if you’re already connected to Allegrow, your mailboxes are checked every hour to ensure they are passing authentication).

DKIM, SPF, and DMARC are critical to demonstrating responsibility as a sender, and it will be challenging to reach high levels of deliverability without all three protocols in place.

So, make sure to follow DMARC reports, check SPF records, and take other steps to improve email performance. This is especially true if you’re in B2B, as many filters/security settings on email servers for mid-market and enterprise businesses prevent emails from being delivered unless they have all three protocols in place.

If you’re unsure how to set up these protocols, you’ll want to start with SPF, following the essential guidance for defining your SPF records here. Then, enter the admin panel relevant to your email provider and DNS to generate and add a DKIM record. After both SPF and DKIM are in place, you can define and roll out your DMARC policy.

4. Use High-Quality Contact Data

Targeting the right prospects at the right companies while avoiding bounces is vital to maintaining a high sender reputation. Using a high-quality contact data provider can help. If you’re not sure where to start or how your current provider stacks up, here are a few of the best:

• ZoomInfo: One of the largest B2B contact information providers, Zoominfo offers leading data coverage while maintaining high quality (including direct mobile numbers). Typically, ZoomInfo is the best choice for mid-market to enterprise sales and marketing teams.
• SalesIntel: This company offers high-quality contact data and a custom research function that allows more significant customers to specify the businesses and job roles they seek. SalesIntel is a top choice for fast-growing teams that use ABM.
• Cognism: Get high-quality contact data specifically for Europe and regions where other providers may lack coverage. This is the best choice for teams with a focus on EMEA as a market.

Most data providers verify their data set every 90 days, which means it’s important to ensure your data is verified before you contact a prospect.

5. Cleanse Data and Automatically Remove Bounces

Bounces happen to every business occasionally. However, sending cold emails sometimes involves guessing or using purchased email lists, which can lead to high volumes of bounces unless precautions are taken. Therefore, email providers have identified high volumes of bounces as one of the main spam signals.

Your overall bounce rate should be less than one percent to avoid getting your domain flagged for spamming. These three steps will help you reduce your email bounce rate:

1. Ensure your cold email system automatically removes contacts from future emails if they bounce. Close CRM has this setting in place by default across all users.
2. Use a data validation provider before adding new contacts to a sequence. List cleaning providers like Hunter verify email addresses and flag those likely to bounce so you can remove them from your list. Remember to verify addresses before sending emails, not just once when you receive the data.
3. Limit the number of email addresses you message at the same company. Corporate spam filters block emails if you contact multiple people in an organization over a short period. These limits can be created in your contact data provider's settings.

6. Write High-Quality Content (and Test it for Spam Filtering)

If your email doesn’t engage prospects or looks like spam, you’ll have difficulty reaching the main inbox. This is why high-quality content tested for spam filtering is vital.

Additionally, crafting compelling email content can be both time-consuming and challenging. Consider using an AI-powered email writer to streamline this process and enhance the quality of your emails. Our AI Email Writer tool can help you create personalized, engaging emails that resonate with your prospects, ensuring your messages stand out in their inbox.

While there’s no specific formula for creating brilliant content, it starts with deeply understanding your prospect and testing different approaches. Here are a few best practices to improve email content quality:

• Relevance/Trigger: Using relevant triggers will help your content stand out. This can’t simply be the size of the prospect's company and industry. Instead, get more specific, such as a specific hire they made recently, the content they engaged with on LinkedIn, or a review they left describing a challenge. You should mention this trigger concisely in your message's first line or two to maximize engagement.
• Length: To count as engagement, the prospect must read 100 percent of your email. If your message is too long, it will get deleted as soon as the prospect opens it. Keeping the first email in your sequence to 50 or fewer increases general engagement.
• Subject line: When it comes to subject lines, boring = better. Yes, that’s right, having a very boring subject line of 4 words or less produces more engagement than one focusing on your product's benefit. This is because you need to get through the prospects' mental spam filter and their real one. If you want to create effective email subject lines that break through those filters, check out Close's Email Subject Line Generator. Or our cold email subject line guide.
• Size/Attachments: Most corporate spam filters automatically flag with attached files. From the spam filter's perspective, this is because the larger a message is, the higher the risk. Avoid attaching files and reduce the size of any images—including your logo in your signature.
• Links: Links can make your message appear more ‘spammy.’ We recommend including two or fewer links in a cold email (this includes any links in your footer).
• Footer format: Keep your footer as simple as possible. Include basic information such as name, job title, company name, website, and address. Including your website will depend on link usage throughout the rest of your email, and you may want to consider adapting your job title in the footer if it’s heavily linked to prospecting—for example, SDRs may want to experiment with listing themselves as a "Partner" or "Associate."
• Simple CTA: To simplify your CTAs, keep them to less than a line and make sure they’re the only line with a question mark to draw attention to the ask. Consider lowering the bar of your ask to simply get a response rather than booking a meeting right away. Gong found that asking for interest in a cold email rather than time is twice as effective.

Finally, use these points as a starting point to create cadences that are more likely to produce engagement–but don’t be afraid to experiment. What works for you might differ from best practices.

7. Consider Setting Sending Limits per Mailbox

In addition to increasing your sending volume over time, you’ll also want to limit outbound emails pre-box or the volume of contacts added to your campaigns to avoid looking spammy.

Getting your daily sending volume per mailbox right is a balancing act. The higher your daily volume, the greater your risk of receiving multiple manual spam reports, which can lead to inbox suspension.

Follow these guidelines for the maximum volume of emails you should send each day from a single mailbox:

You might be wondering - does this mean it is never safe to send 800 emails per day? The answer is you can, but if you have existing mailboxes and domains, you want to spread this activity across ten mailboxes based on the "Safe" guidance above.

Note that the maximum volumes we advise for each mailbox vary based on how aggressive/open to risk you are and the type of mailbox you use. We assume no one conducting cold outreach uses a free email such as an @gmail.com account - as our guidance is only for commercial users. (Never cold email from a free email account)

8. Send Cold Emails on Subdomains (or Other Root Domains) at Scale

Sending cold emails specifically from different subdomains or root domains altogether has become a common best practice in recent years. This allows you to have greater control and visibility over the sender reputation of the domain used for prospecting.

Using a different domain or subdomain also decreases the risk for your entire strategy because you aren’t putting all your eggs in one basket. Below is a breakdown of how an email address is made up:

Regardless of how careful you are, there is always some risk for your sender's reputation when sending cold emails. As email providers primarily categorize sender reception on a domain basis, using your core domain could impact other business operations and is a considerable inconvenience to migrate away from in general.

Therefore, using different subdomains and domains lets you hedge your bets and ensure communication to inbound leads and customers receives the maximum level of engagement.

This approach takes a bit more effort but is worth the investment if you plan to scale out to thousands of cold emails each month. Plus, you’re in good company; brands like Apple, Gong, Asana, and Allbirds use subdomains for their email marketing.

9. Use Multi-Channel Sequences for Maximum Engagement

Email will always be your top outreach channel, but it’s vitally important to maximize engagement across your sequences, so email isn’t your ONLY outreach channel.

Why? Using multiple channels increases your exposure to prospects and the number of follow-ups you can send a single contact without increasing your spam risk. It’s no secret that the more unanswered follow-ups you send to a prospect, the more likely they are to report your messages as spam manually. Using multiple channels helps increase familiarity and maximizes your engagement without increasing email volume.

Examples of some of the main channels you’ll want to add to your sequences if you aren’t already using them:

LinkedIn Connection Requests + DMs: Executing LinkedIn prospecting correctly is important. Rather than just connecting and pitching, aim to get a response and build engagement:

Calls: Some sales teams avoid making outbound calls, but they still work well. This distinguishes you from companies that are too scared to start a conversation.

Direct Mail: Services like Alyce and Reachdesk allow you to send packages during prospecting. This is a great fit for accounts you expect to convert to high-value customers. Increased engagement on these key accounts will help improve the reputation of your domain, so even the communications you send to prospects who aren’t receiving these gifts are likely to be more impactful.

Voice notes / Videos: Creating personalized voice messages from a script makes you seem more human, which is one of the fundamental steps to getting a response and more engagement:

Social Selling: This subject gets a lot of hype, but people rarely do it authentically inside a sequence. Here’s a great example: We were in the sales process for Nylas when their AE noticed our company was hiring and posted the following message:

This was just one more touch point to keep their proposal top of mind without sending a follow-up message.

The key to doing this consistently is to add a task step in your cadence to review the prospect's company and contact profiles on Twitter and LinkedIn and then share/comment genuinely on something they post.

10. Use a Warm, Personal Tone in Follow-up Emails

Usually, the quality of follow-up emails has a severe drop-off compared to the opening email in the sequence.

I often get a few emails every day that say something along the lines of, ‘Did you see my last email?’, ‘I didn’t hear back from you’ or ‘Thoughts?’ Some of these emails used to work well (I’ve been guilty of a few one-line follow-ups in the past), but in 2024 it's overused and annoying–and likely to land your email in the spam folder.

The primary issue with these cold, short follow-ups is that they focus on you rather than the prospect. Shorter follow-up emails are 15 times less likely to help you book a meeting.

To keep your follow-up emails a bit warmer, here are some examples of the kinds of changes you could make to your current follow-up sequence:

Follow-up 1: change "Did you see my last email" to "Would you say you’re similar to XYZ?":

Follow-up 2: Change "I’ve reached out to you a couple of times" to "Did you notice a change when ABC occurred?":

Follow-up 3: Change "Break-up email" to "I made a mistake - is X more focused on this:"

By bringing your follow-up emails up to the same standard as your initial email and avoiding a pestering tone, you’re more likely to get a response.

11. Create a Disengagement Trigger

The more disengaged your list, the worse your sender reputation will be. Top-performing senders optimize messages to maximize engagement on each email they send.

The most common mistake related to engagement is continuing to message contacts after they’ve become disengaged. Keeping contacts on a list after they’ve stopped listening can cost you deliverability to new prospects who may be a better fit and more engaged. We call this disengaged segment "dead weight."

The obvious solution is to remove disengaged contacts from your list. But judging when someone becomes disengaged is easier said than done.

Here are some general best practices to know when to stop sending prospects emails:

How you enforce these rules will depend on your CRM/sales engagement solution. In Close CRM, for example, this can be achieved using SmartViews to regularly segment contacts that meet those criteria and remove them from sequences in bulk:

Implementing these rules increases general engagement and reduces the risk of contacts reporting your emails as spam. This leads to a better overall score and a more effective warm-up process on your domain.

12. Send Emails Individually, Not Through a Third-Party SMTP

To get the highest open and reply rates, you’ll want to send emails one-to-one through Google Workplace or O365 email accounts expressly set up for prospecting. You won’t want to use a third-party delivery service / SMTP server for cold email.

Using a third-party SMTP means sending emails through a server/service like AWS or SendGrid, intended for opt-in communications, and email providers scrutinize content from third-party SMTP servers more closely than individual email accounts.

Email providers are more likely to heavily filter content sent via third-party servers because third-party servers can deliver emails to an unlimited number of recipients over a short period of time, which is far more likely to be used for mass spamming and phishing campaigns than one-to-one emails.

To check if your current setup is running through a third-party server, check the folder sent to your cold email mailboxes. If you see messages being sent individually, you’re using one-to-one outreach (as we’d advise). If you can’t see the messages you sent anywhere, you’re probably on a third-party service and will need to move towards using your email client directly.

Moving to one-to-one outreach vastly reduces your volume and increases the time it takes to contact every prospect. However, you’ll yield better long-term results!

13. Monitor Spam Reporting in Google Postmaster Tools

Google Postmaster Tools (GPT) helps you monitor the sentiment of prospects who use GSuite. Since Google is one of the most popular email providers, especially in the B2B segment, this is a great resource for determining whether people react negatively to your messages.

Note: GPT will not provide data on the percentage of your emails being automatically filtered into spam (you’ll need an inbox placement provider to figure that out), but it can give you an idea of how many prospects manually flag your messages as spam.

This can help you understand if the messages/follow-ups you’re sending are too aggressive so you can adapt your approach when you see spikes. One of the biggest issues with relying solely on GPT is if messages are automatically filtered to spam, you’re not likely to see any spikes in reports (because people can’t manually report emails as spam if they're already in that folder!)

14. Always A/B Test Your Cold Emails

Running consistent A/B tests will help your cold outreach activity look less robotic and prevent content from becoming stale. There are two primary types of A/B tests to be aware of and use:

1. Live Variations: Send multiple versions of the same email to prospects in real time. To do this, create an alternative version of your template directly in your sales engagement platform and add it to your sequence:

2. New Structure Tests: Testing a new structure involves creating an alternative version of your email, usually with more drastic changes (e.g., eliminating all links). Applications like Allegrow let you test how often each version is filtered into spam, which can help firm up the technical soundness of these drastic changes before they go live (as you ideally don’t want to be practicing on your prospects):

Start by implementing around three live variations for the same sequence email to test prospects' sentiment towards it (i.e., tracking which receives more positive responses). You’ll want to conduct new structure tests every 30 days, with the goal of changing your overall template at least every 60 days to avoid your messages getting stale.

Results from (Real) Email Warm Up Campaigns that Work

Campaigns with a quality warm-up provider result in higher open and response rates. Close user Ramzi Malas from Lux Sales Consulting saw their open rates increase 30-50 percent using Allegrow for email warm-up:

FAQs About Warming Up Email Accounts Before Outreach

What makes a quality email warm up provider?

There are several key functionalities the best top warm up providers offer, and without them, you’ll be at a disadvantage. These include:

• Real Business Domains (not fake seed accounts): A lot of warm up platforms use "seed accounts" / ‘private networks’, which are purchased or set up in bulk by the warm up provider. The problem is those email addresses are not unique domains or made from real business inboxes (ESPs know when an account is fake.) Therefore, the data on inbox placement is inaccurate and doesn’t help improve inbox placement. Other providers like Allegrow build their network from thousands of unique B2B inboxes (meaning other Allegrow users' real inboxes!) so the network can simulate engagements safely and provide accurate data across the board.
• Significant sample size: Many testing platforms either send a low volume of emails, meaning under 100, and calculate reputation from this data or send one batch of emails rather than continually sending emails over time and calculating an average reputation score based on multiple data points. These solutions will be ok to use for free if you’re just getting started. However, if you’re a pro marketer, these sample sizes aren’t statistically relevant compared to the number of emails you send.
• Separate monitoring and interaction relationships: Some warm up tools use the same domains to measure reputation and engagement. This means the email domains that respond to your emails, move them out of spam, mark them as important and so on, are the same domains that calculate your email reputation over time. The issue is that email domains have a ‘memory.’ Meaning, if you have a low reputation and send an email to me tomorrow that lands in spam but I move your email out of spam, even if your reputation rate doesn’t change, future emails you send to my inbox are unlikely to land in spam as my preference to interact with you is remembered. Therefore, platforms that use the same mailboxes for both interacting and monitoring will inevitably show less accurate reputation data over time. Separating monitoring relationships from interaction relationships means your data will be accurate in the long term.
• Content testing: How do you keep getting benefits from inbox placement/warm up tools if your sender reputation is above average? With most warm up providers, that’s where the journey ends. However, the best email warm up content providers also offer content testing, which allows you to test different variations of your content against real B2B inboxes and compare where email providers place each version. This feature helps you improve your email marketing long-term.

What is a good open and response rate for cold email?

Email open rates of above 27 percent are average, with top-performing outreach sequences hitting 50% or higher. Response rates of 12 percent or more across your sequence show you’re engaging with the right prospects and have good inbox placement.

Looking to enhance your B2B outreach? Check out our article on 12 B2B Cold Email Templates, where we explore the nuances of creating effective b2b cold email templates.

How do I integrate an email warm up tool with my CRM / Sales Engagement?

Check with the specific warm up provider you’re using to see how well they work alongside your email provider and Sales Engagement platform. As an example, Allegrow integrates with all major email providers for B2B users and directly integrates to Close Instructions on setting up the integration are available here.

As a marketer, your CRM platform plays a crucial role in your ability to reach and engage with your target audience. Learn about the best CRMs for marketers in this article.

How long does it take to warm up an email?

Email warm up is not something you do once and then are done. To reach a high level, you’ll need to continue training/conducting the process in the long term. For best results, start using a quality warm up system at least 30-days before starting outreach and continue warming up for as long as your domain is used for sales and marketing.

How can I calculate what percentage of my emails land in spam?

Some sending platforms provide ‘spam reports’ or ‘undeliverable’ / ‘bounce reports’. These do not tell you how many emails land in spam folders. That's because the majority of emails that land in spam are automatically filtered. The only way to see how many emails land in spam is to monitor where. Warm up solutions do this in three steps:

1. Emails are sent from inboxes on your domain to external emails.
2. The provider is connected to these inboxes so they can check where emails land. (This means they can count the quantity that landed in spam, promotion, junk, or unfocused folders.)

The volume of emails that lands in these folders compared to the overall volume sent is turned into a reputation percentage and reported back to you.