What are the implications of sharing a subdomain between two different ESPs?

Email marketer from GlockApps answers that sharing subdomains between different email service providers can affect your sender reputation. If one ESP has bad email practices and their IP addresses get blacklisted, it can have a knock-on effect on deliverability for others using the same subdomain.

Email marketer from Mailjet Blog explains that sharing a subdomain between multiple ESPs can create deliverability issues. It becomes harder to isolate reputation problems, impacting sending volume and inbox placement. Mailjet recommends dedicated subdomains for each ESP to maintain control and identify issues.

Marketer from Email Geeks explains that if the current ESP: a) is controlling the DNS, b) allows you to make changes, c) the From domain is not the same as the return-path, d) the new ESP doesn't need to monitor replies to messages, and e) the new ESP doesn't want to control the DNS too - then in theory there should be no issues. It should work for the From (5322.From) domain but not for the return-path (5321.MAILFROM) domain. It's not an ideal setup because the current ESP could make changes to the DNS without telling you and using a different From domain with the new ESP is preferred.

Email marketer from Reddit shares that deliverability issues can arise from shared subdomains. If one ESP has poor sending practices, it can negatively impact the shared subdomain's reputation, affecting deliverability for all ESPs using it. Using distinct subdomains isolates these issues.

Marketer from Email Geeks shares that when you share a sending domain, it's harder to identify what stream is influencing what to find and resolve a problem. If they want to share the vanity domain, it's easy enough so long as the other domains in use are unique or use unique selectors AND you have a way to manage all entries.

Email marketer from StackOverflow answers that SPF records can become complex when sharing a subdomain. Each ESP requires its own SPF record entries, increasing the risk of exceeding the DNS lookup limit. This complexity can lead to authentication failures and deliverability problems.

Email marketer from SendGrid explains that using different subdomains for different types of email (transactional vs. marketing) is a best practice. This can be extended to using different subdomains for different ESPs. This allows you to isolate and manage the reputation of each sender separately, preventing issues from one ESP affecting the performance of another.

Email marketer from Litmus shares that segmenting email traffic using subdomains for different email types or ESPs helps protect sender reputation. This strategy isolates potential deliverability issues, preventing one ESP's problems from affecting the overall domain reputation.

Email marketer from MailerCheck explains that deliverability rates can be negatively impacted if using the same subdomain across two different ESPs. The main concern here is if one vendor suddenly suffers a blow to its sender reputation. If you use them to send emails from the same subdomain, it can undermine your deliverability rates.

Email marketer from Email on Acid explains that one of the primary concerns with sharing a subdomain is maintaining a consistent sender reputation. If one ESP experiences deliverability issues, it can negatively impact the reputation of the entire subdomain, affecting email delivery for all users.

Email marketer from Reddit explains that using different ESPs on the same subdomain can complicate email authentication. SPF records may require frequent updates, and DMARC policies must be carefully configured to avoid deliverability issues.

Marketer from Email Geeks shares that they are servicing multiple senders sharing subdomains between ESPs. They also do not recommend it, but when clients push against their recommendations they do it. They state that as long as the a)-e) criteria Ken mentioned are met senders do not seem to have any issues.

Marketer from Email Geeks explains that if Platform A is controlling the DNS for the From (5322.From) domain, you likely can't share it with Platform B because you would need to create additional DNS records to accommodate Platform B, which you can't do. Also ESPs often want to control the DNS for the return-path (5321.MAILFROM) domain so that they can track bounces.

Email marketer from SparkPost explains that sharing a domain (or subdomain) across multiple ESPs can dilute your sending reputation. Each ESP will have its own sending practices and authentication configurations. Disparate practices across the same subdomain can lead to inconsistent sender signals, making it harder for mailbox providers to trust your mail.

Expert from Spamresource explains that you should avoid using the same sending address and subdomain across multiple email marketing platforms. If you do the reputation of one platform will have a negative impact on the other.

Expert from Word to the Wise explains that sharing subdomains across multiple ESPs can negatively impact sender reputation. Each ESP's sending practices affect the subdomain's overall reputation, making it difficult to isolate and address issues. Dedicated subdomains allow for better management and control.

Documentation from DMARC Standard explains that implementing DMARC policies becomes complicated when sharing a subdomain. You must ensure alignment for all ESPs. Monitoring and reporting also become harder, making it difficult to identify and address deliverability issues.

Documentation from RFC explains that subdomain delegation allows splitting a domain into multiple zones, which could be used for different ESPs. If each ESP has it's own subdomain, this can allow the full DNS control they require without conflicting with others. However the RFC does not address shared subdomain scenarios.

Documentation from DKIM Standard explains that each ESP should use its own DKIM key. Sharing a subdomain requires managing multiple DKIM keys, which can be complex. Incorrect key management can lead to authentication failures.

Documentation from Microsoft answers that when configuring your domain to send email from Office 365, you might need to update several DNS records including SPF records. When you use more than one sender, keeping these up to date can be difficult and can result in the SPF failing and impacting deliverability.