Does a bad reputation of one sub-domain impact the reputation of other sub-domains?

A common method to protect your sender reputation is to use separate sub-domains for different mailings. 

Sub-domains are often treated as a separate domain name by most inbox providers and email service providers. This allows for a variety of benefits for email marketers or business owners, such as maintaining a separate reputation for large promotional emails vs. customer-only emails. 

However, some sending practices can cause a negative reputation to affect other sub-domains. This kind of segmentation is not a surefire way to keep separate sender reputations for different lists, but it can help.

Why use sub-domains for different email lists or types of emails?

Most inbox providers, spam filters, and blacklists treat a sub-domain as a separate entity with its own reputation. Maintaining a high sender reputation means your emails are more likely to be delivered and end up in the user's primary inbox, and are less likely to end up in spam. 

Using separate sub-domains for various types of emails in your organization can help protect your sending reputation. 

For example, you might have separate sub-domains for promotional emails and transactional emails, allowing you to ensure transactional emails like receipts or password reset emails are not impacted by the deliverability of promotional emails. 

While there is sometimes an impact on reputation between sub-domains, it’s usually small. Only consistently poor sending practices can cause a sub-domains reputation to impact other sub-domains reputation.

What kind of sending practices can cause sub-domains to impact each other? 

Typically inboxing issues with one sub-domain will be isolated, and won’t bleed over to other sub-domains. However certain sending practices can cause issues for an entire organization’s sub-domains. 

These include:

• Frequently sending to large numbers of email addresses that are not opted-in.

• Aggressive sending practices with poor engagement rates over a long period of time.

• Lack of authentication that allows malicious actors to send fake emails from your domain.

• Poor sending practices over a long period of time from the top-level domain. 

• And more. 

In short: if you want to maintain a great reputation across multiple sub-domains, use them for specific segments of your email list, and don’t be spammy. Most sub-domains have their own reputation, but poor sending practices over a long period of time can have a negative impact across your organization.