Server Fault is a question and answer site for system and network administrators. It's 100% free, no registration required.

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

I am trying to setup Postfix a few different domains on a virtual host.

I need to have email setup just to send out registration confirmations and new password requests. No one will have a mailbox on this server.

It seems this means that I want to setup Postfix as SMTP only.

I've also read about configuring Postfix null clients for simular needs.

What is the difference between Postfix null client and SMTP only?

share|improve this question
What's "simular", is that like a similar simulation? – Chris S Jun 29 '11 at 12:26
The more interesting question, raised by Cucumber below (who then suffered for it), is what Bryan Wheelock thinks "SMTP Only" is. Who told you that Postfix would be "SMTP Only", M. Wheelock, and what did that person think that xe meant by that? Because at the moment you're asking us to tell you what the difference is between a null client and "Blue Hairy Penguin Mode". We can tell you about null clients, and not being the final destination for any domain, but not about things with ambiguous definitions. – JdeBP Jun 29 '11 at 15:53
"SMTP only" was a term I ran into online reading some tutorials. I wasn't sure what it meant. I wanted clarification. Thanks. – BryanWheelock Jul 12 '11 at 15:31
up vote 3 down vote accepted

Postfix Null clients means there are no local clients that it delivers email for. So you can still send email over it, but email is never going to traverse its way back to you via that server.

An SMTP only server can also be a null client server. Since SMTP is only for outgoing email a user could never pick the email up via POP/IMAP etc. But this machine could still be responsible for the email, so it is in my mind not always a null client server. For example email could be passed from here to an exchange server. So in that use case, the SMTP Only server is not just a null client server.

share|improve this answer
You exemplify exactly why this question is unanswerable. You've had to invent a definition of what "SMTP Only" is, in order to then compare it to a null client. It's not even a well-founded invention. SMTP is not "only for outgoing mail". After all, SMTP Relay is how incoming mail most often reaches a machine. It's not unreasonable to suppose an alternative definition of "SMTP Only" where Postfix "only" runs the SMTP Relay client and the SMTP Relay server (and not, say, the LMTP client or the QMQP server). – JdeBP Jun 29 '11 at 16:00
I changed my wording a little to make it easier to understand, I guess I was not successful. By outgoing only I meant that it does not handle traffic between MUA and server directly. – SuperBOB Jun 29 '11 at 16:13
JdeBP, I actually think the question is reasonable. Both terms have been encountered by the OP and he wants to rationalise them a bit. I attempted to help him do so. I would say that it is at least as useful to further ground his understanding of the terminology/technology, than it is to fault the foundation of his question. I believe the former is more constructive. By pitching my answer at the the audience whilst still I would argue being technically accurate, I thought I was helping as best I could. – SuperBOB Jun 29 '11 at 16:17
Inventing things from whole cloth in order to fill in holes in the question isn't "further grounding his understanding of the terminology/technology". It's only piling on the confusion yet further. M. Wheelock goes away thinking that there indeed is such a thing as "SMTP only" mode, and that a nonce definition pulled from thin air is what it is. Painting this as "more constructive" is ridiculous. M. Wheelock is worse off for it at the end of the process, not better. – JdeBP Jun 29 '11 at 16:35
I disagree, but thanks for your comments ill take it into account in the future. I think you have been little combative, your posts are reading quite aggressive - we are all here to help each other after all. Anyway, enjoy Sir! – SuperBOB Jun 30 '11 at 9:43

what is a setting "SMTP only"? There is no any reference about it on official site postfix.conf.5 and You can don't setup other protocol (pop3 or imap), and then it will be "only smtp".

If you want to use your server only for sending service information, you cat use Postfix on a null_client

share|improve this answer
Hes not asking how to achieve an SMTP Only setup hes asking what the difference is between the two terms hes encountered. – SuperBOB Jun 29 '11 at 15:16
You haven't appreciated Cucumber's good point. If the notion of "SMTP Only" doesn't have a formal definition, then it's meaningless to ask how it differs from something else. – JdeBP Jun 29 '11 at 15:41
I found it quite hard to read Cucumber's post so its possible I missed something useful, apologies to you Cucumber! – SuperBOB Jun 30 '11 at 9:46
all right, my English needs to be improvement. – Cucumber Jun 30 '11 at 11:22

Your Answer


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

Not the answer you're looking for? Browse other questions tagged or ask your own question.