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Assume I own the domain name, I am creating a setup where I receive email sent to using Google Apps. The MX records for already point to Google's servers and it works great. Now, I have an application server where I would like to send out automated emails, such as notifications about user activity, etc. I may also use this server to send bulk emails such as newsletters (legitimately, of course). Here, I have the option to use a subdomain for all of my automated outgoing email. Perhaps I can send these emails from and set the Reply-To header to, which would then be directed to my Google account for a real person to answer.

My question is: Is there any added benefit of sending automated email from an email address with a subdomain?

Note: I have already taken measures to use SPF and DKIM to authenticate my email from the application server. I have heard that some receiving mail servers also do a reverse MX check to determine whether your email is spam. If this is true(?), I'm assuming a subdomain would be useful because I can then make a separate MX record for to point to my application server, while keeping the other MX's for on Google.

Aside from that, is there any other reason I would use a subdomain? I notice this is commonly used in email from Groupon, Southwest Airlines, Office depot, and countless other newsletter services (sometimes they use entirely different domains), and I haven't been able to figure out why.

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You do not need a MX record to send mail. – gparent Sep 7 '13 at 0:53
I understand that an MX record is not necessary to send mail, but should I worry about receiving mail servers performing a reverse MX check and finding the IP of the MX to be different from where the email was sent from? – Michael Brook Sep 7 '13 at 2:28
You don't need to write your SPF record against the MX record. You can also use IP addresses. – gparent Sep 7 '13 at 16:45
If you don't need an MX record, what happens when the machine receiving the email is not in the domain that is being addressed? – Avery Payne Mar 9 '15 at 18:07
up vote 1 down vote accepted

My question is: Is there any added benefit of sending automated email from an email address with a subdomain?

I don't think there are many technical reasons why a subdomain is required or necessarily better for deliverability of emails.

That being said, having/using subdomains can sometimes make things easier for large organizations because:

  • As an admin, I may not have access to global resources associated with the primary domain. For example, maybe I only manage IPs/Firewalls/DNS Zones in my specific regional office/division.
  • Even if I did have access to global resources, the scope of users/systems affected by my email changes is large. Perhaps I don't want that.
  • Even though we're specifically discussing outbound deliverability here, there is still the possibility of NDRs and failed delivery generating return traffic. Depending on the volume of mail I'm sending, I may not want delivery status notifications going back through my standard inbound mail route.

Ultimately, I think it comes down to the use case here and scope of systems affected.

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A big advantage is that most email spammer-blacklist organizations treat subdomains separately. So, even if your automated e-mail subdomain gets blocklisted (PC term for blacklist), your main domain will still be able to continue sending e-mails. This is actually pretty important, because even the most innocent newsletters/automated replies get flaged as spam by some receivers. And this can eventually lead to being blocklisted.

Also, having a subdomain makes tracking reputation separately possible.

An interesting interview can be found here with spamhaus: Spamhaus Provides Answers Part 4

Question number 32 is talking about subdomains and how they are treated separately (unless more subdomains from the same domain get blocklisted, which might lead to the whole domain getting blocklisted).

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