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I want to send email via postfix (according to the send-only "null" configuration example given in the postfix documentation) from a host that does not have a proper DNS record, MX or otherwise; in fact the IP address may not even be static (say, a home cable/DSL connection). Does this increase the chance of the receiving mail server flagging messages from this host as spam, since probably most spam in the world comes from similar hosts that have been compromised by spammers? I am only planning on sending a few messages per day, to email addresses I own.

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Q: Is it ok to send mail from a domain with no MX record? A: Yes it is. An MX record determines where email is delivered to, not where it is sent from. What you need is an SPF record for your sending MTA. –  joeqwerty Aug 1 '13 at 21:58
    
You would probably do better here digging to the root of your problem. At a guess, I'd say you have some software deployed in small offices across the country that you want to email you status reports daily and you won't know the office's SMTP server details. If that's your problem, there is a better solution. Whatever your real problem is, there's probably a better solution. –  Ladadadada Aug 1 '13 at 21:58
    
@joeqwerty - I was wondering if common spam filtering software would use the existence (or not) of a MX record for the sender as a heuristic in determining if a particular message is spam... ie, it'd be obvious something is wrong if a million messages claiming to be from diff addresses are coming from a comcast home cable line. I will look up SPF records, never heard of it. –  user2243865 Aug 1 '13 at 22:15
    
@Ladadadada - yes, I'm looking into nagios and a few others, but for example mdadm (linux's software raid manager) has built-in ability to send email on emergency... I primarily want to know if I can start using such features without worrying about DNS and such thing external to the machine I'm configuring, which I may not have control over. –  user2243865 Aug 1 '13 at 22:16
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3 Answers 3

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No MX record will probably be fine.

Not having a proper reverse DNS and coming from some home ISP IP ranges will get some messages marked as spam. Especially if there have been actual spammers coming from that particular netblock.

The best thing to do would probably be to use a smarthost that you control to ensure the messages get delivered. Make it run on a port other that 25 as some ISPs block port 25 to anything but their own mail servers.

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The answer is: Yes it is okay. But you should:

Have a reverse DNS (PTR) record for your mail server. Your Hosting Provider must set although most cloud providers give you an interface to do it yourself.

Have an SPF (TXT) record as joeqwerty mentioned.

DKIM-sign your emails (also requires a TXT record). See OpenDKIM or dkimproxy.

And depending on how important your email reputation is you may want to consider Return Path certification.

Cheers

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Yes, but without MX record and rdns your mails may bounce, or it may consider as spam mail. and filtered by advance mailscanner or discard by mailserver.

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