Will a new subdomain protect my main domain from old contacts?

Not necessarily. A new subdomain will still need its own warm-up process. Using a new subdomain for old, unengaged contacts can lead to poor reputation for that subdomain, making it difficult to use for future sends. Focus instead on cleaning and segmenting your existing list.

How should I approach sending to contacts who haven't received emails in over 6 months?

It's best to segment your old contacts by their last engagement. Start with those who were most recently active (e.g., 6-12 months ago) with highly relevant content. For very old or unengaged contacts, consider removing them or using a list cleaning service before any sends.

What are the risks of sending emails to very old or unengaged contacts?

Sending to dormant addresses increases the risk of hitting spam traps, leading to blocklisting (or blacklisting) and a damaged sender reputation. It also results in low engagement, signaling to ISPs that your content isn't relevant, which can cause future emails to land in spam folders.

What is email warm-up and why is it important?

A warm-up is a gradual increase in email volume from a new domain or IP address to build a positive sender reputation with ISPs. This process is crucial because new sending entities lack historical data, and sudden high volumes can trigger spam filters.

Should I use a new subdomain to warm up old contacts? - Sender reputation - Email deliverability - Knowledge base

I've encountered this question many times, and it's a critical one for anyone managing email lists, especially those with segments that haven't been touched in a while. The natural inclination when facing a potentially risky send, like warming up old contacts, is to create some distance between that activity and your primary sending reputation. This often leads to considering a new subdomain.

The idea is simple: if the old contacts perform poorly (high bounces, low engagement, spam complaints), the damage is contained to the new subdomain, leaving your main domain's reputation intact. However, the reality of email deliverability is more nuanced than that. A new subdomain isn't a magic bullet that allows you to bypass the rules of sender reputation.

In most cases, creating a new subdomain specifically to warm up (or re-engage) old contacts is not the recommended approach. This strategy can introduce more problems than it solves, primarily because new subdomains still require their own dedicated warm-up process.

The risks of sending to old contacts

Sending emails to old, unengaged contacts, especially those who haven't received mail in six months or more, carries significant risks. Over time, email addresses can become inactive, turn into spam traps, or simply be abandoned by their users. Sending to these addresses can severely harm your sender reputation.

Spam traps are a particular concern. These are email addresses designed to catch spammers. Hitting a spam trap can quickly get your sending domain or IP address listed on a blocklist (or blacklist), leading to widespread email deliverability issues. Even if you avoid spam traps, low engagement rates from old contacts can signal to Internet Service Providers (ISPs) that your emails are not valuable, causing them to route your messages to the spam folder or reject them entirely. It's crucial to understand when to consider an email warm-up.

The problem isn't just about avoiding a blocklist, but also about maintaining a positive sender reputation that ensures your emails reach the inbox consistently. ISPs like

Google and

Yahoo heavily rely on engagement metrics to determine your sending credibility. Sending to a list that is likely to have a high percentage of non-responders can swiftly downgrade your reputation, affecting all future sends, regardless of the list quality.

This challenge highlights the need for a careful strategy when dealing with dormant or unengaged segments. The goal should be to re-engage these contacts responsibly or, if they prove too risky, to remove them from your active sending lists. Protecting your primary domain from harm is paramount for long-term email marketing success.

Why a new subdomain isn't a silver bullet

While the idea of isolating risk with a new subdomain is appealing, it's crucial to understand what a new subdomain entails. A new subdomain, even if part of an already warmed root domain, starts with its own, completely fresh reputation. This means it requires its own warm-up process for email sending.

Warming up a subdomain involves gradually increasing sending volume to highly engaged recipients to build trust with ISPs. This process is time-consuming and requires sending to known good, active email addresses. If you're planning to use this new subdomain for old, potentially unengaged contacts, you'd be attempting to warm it up with the very data that is likely to generate poor engagement, bounces, and complaints. This counteracts the entire purpose of a warm-up, likely hindering the subdomain from ever achieving a good reputation.

A new subdomain does provide a separate reputation, which can be beneficial for segmenting different types of email traffic (e.g., transactional vs. marketing). However, for a list of old, risky contacts, it simply shifts the reputation problem rather than solving it. Warming up a new domain is essential for building sender trust.

Sending from your main domain

Reputation risk: Directly impacts your primary sender reputation if performance is poor.
Deliverability: A negative impact here affects all future campaigns sent from this domain.
Effort: No additional warm-up needed for the domain itself, but careful segmentation is essential.

Sending from a new subdomain

Reputation risk: Isolates risk from your main domain, but the new subdomain will suffer.
Deliverability: New subdomain needs its own warm-up, which is difficult with old contacts.
Effort: Requires a full warm-up process for the new subdomain before any meaningful sends.

Smart strategies for old contacts

Instead of creating a new subdomain, the focus should be on strategic list management and re-engagement. If you have contacts that haven't been emailed in over six months, the first step is to consider their engagement level before you stopped sending. Were they highly engaged before going dormant, or were they already slipping away?

I recommend segmenting these old contacts based on their last known activity. For instance, divide them into groups: those who opened or clicked within the last 6-12 months, those who last engaged 1-2 years ago, and those who have never engaged or haven't in over 2 years. This segmentation allows for a more targeted and less risky approach. If you are switching to a new subdomain, remember that a warm-up process is required.

For the most recently engaged segment (6-12 months), you can try a cautious re-engagement campaign from your main sending domain. Start with a very small volume, craft highly compelling and relevant content, and monitor your engagement metrics closely. Be prepared to stop sending to this segment if you see a spike in bounces, complaints, or a significant drop in engagement.

List hygiene and risk mitigation

For contacts older than 12 months, especially those with no recorded engagement, it's generally safer to consider them inactive. Sending to these addresses risks hurting your overall sender reputation. Before even thinking about sending, it's crucial to clean your list thoroughly.

List cleaning services can help identify invalid email addresses, known spam traps, and unengaged subscribers, significantly reducing your risk. While these services aren't perfect, they can help you remove the riskiest addresses before you send a single email. This is a critical step, as many old contacts might no longer be valid or could have been converted into spam traps.

Best practices for old contacts

Segment your list: Divide contacts by recency of engagement. Prioritize the most recently active.
Clean your list: Use a reputable list cleaning service to remove invalid addresses and spam traps.
Craft engaging content: Send highly relevant content to encourage re-engagement.
Monitor metrics closely: Watch bounce rates, spam complaints, and engagement. Stop if metrics are poor.

Remember, the goal is to protect your overall sender reputation. If the risk of sending to old contacts outweighs the potential reward of re-engaging them, it's often better to let those contacts go. Focus on building and nurturing a highly engaged, permission-based list that contributes positively to your email program.

Views from the trenches

Best practices

Maintain consistent sending volumes to build a reliable sender reputation over time.

Regularly clean your email lists to remove inactive subscribers and potential spam traps.

Segment your audience based on engagement levels, sending more frequently to active users.

Prioritize sending relevant and valuable content to encourage sustained engagement.

Common pitfalls

Sending to very old, unengaged contacts without prior list cleaning or segmentation.

Failing to monitor engagement metrics closely after re-engagement campaigns.

Trying to warm up a new subdomain with a list of low-quality, unengaged contacts.

Ignoring high bounce rates or spam complaints from specific email segments.

Expert tips

Always prioritize list quality over quantity to ensure high deliverability.

Consider a re-permission campaign for very old contacts to confirm their interest.

Use email validation services before sending to dormant segments to reduce risk.

If contacts haven't engaged in years, it's often best to remove them entirely.

Expert view

Expert from Email Geeks says not to create a new subdomain for mail that is expected to perform poorly. If there's minimal risk, integrate them with higher-performing traffic to mitigate issues. If the risk is high, it's best not to send to them at all.

2022-11-18 - Email Geeks

Expert view

Expert from Email Geeks says new subdomains require a warm-up, so using unengaged data on a fresh subdomain would prevent it from ever establishing a good reputation.

2022-11-18 - Email Geeks

Final thoughts on warming old contacts

For warming up old contacts, creating a new subdomain generally isn't the solution. It introduces an additional warm-up requirement for the new subdomain itself, which would be challenging to achieve with a list of unengaged email addresses. The risks of sending to dormant contacts, such as hitting spam traps or incurring high bounce rates, remain whether you use your main domain or a fresh subdomain.

The more effective approach is to carefully segment your old contacts, focusing on the most recently engaged ones for re-engagement attempts. Prioritize thorough list cleaning to remove invalid email addresses and known spam traps, thereby safeguarding your sender reputation. For contacts with very low or no recent engagement, it's often best to suppress them from your active sending lists to prevent deliverability issues.