Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Do outgoing SMTP servers need to have assigned domains?

If a domain name is not assigned to an outgoing SMTP server will it increase the spam score?

share|improve this question
up vote 1 down vote accepted

Yes. Many sites will reject mail from you if your mail servers IP address does not resolve to a hostname.

share|improve this answer
According to RFC2821, it is not required. It's helpful, but not required. – joeqwerty Jan 10 '10 at 2:13
Helpful is an understatement. – user17642 Jan 10 '10 at 3:01
the SMTP RFC does not sufficiently explain the complexities of an SMTP server in the real world. – Justin Jan 10 '10 at 3:19
Well it's not its' purpose to explain those complexities. It's purpose is to define a standard. How that standard is implemented is up to software developer. – joeqwerty Jan 10 '10 at 4:32
@Justin: I hear you but that wasn't the question that was asked. The question asked was "Is it required?" and the answer is no. You're correct that it can cause problems, but the OP didn't ask that. I'm not picking a fight I'm just answering the question that was asked: Is it required? No, it's not. The next question the OP should ask is "Can it cause problems if it doesn't?". The answer to that is yes, as you've stated. The best answer would have been a combination of your answer and mine: No, it.s not required but here's what can happen if it doesn't..." – joeqwerty Jan 10 '10 at 16:16

They don't need to have them per any standard in existence - however, as any mail admin with any experience would be able to tell you, a vast amount of anti-spam systems do use the lack of a reverse record as a reason for negatively scoring an SMTP relay.

Which means, the answer to the question in your title is - generally, yes.

share|improve this answer

It's not required as far as I know, but it can help.

share|improve this answer
very ambiguous answer.. domains cost money so I need to know for sure. but thanks anyway! – zimekzimny Jan 10 '10 at 1:39
No, they're not required, but as joeqwerty said, they're very helpful. They don't need their own domain - they can be assigned a subdomain (e.g. If the forward and reverse dns for your SMTP servers don't match, the mail has a very high probability of getting tagged as spam. – EEAA Jan 10 '10 at 1:59
How is it ambiguous? You asked what I interpreted as a yes or no question and I gave you a yes or no answer. No, they are not required as far as I know. It is helpful in order to keep you off of blocklists, but it's not required. If you'd like yo know for sure then read RFC2821, which is what I did and I don't see anything that implies that an assigned domain is required. – joeqwerty Jan 10 '10 at 2:13
thanks guys, actually assigning it to a subdomain is the solution here... – zimekzimny Jan 10 '10 at 11:56

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.