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I'm really confused about the MX Records and generally with email. I've set up Haraka SMTP server for outbound email delivery because I need to send sign up validation emails.

If I don't want to receive emails just to send them, do I need to setup MX records for my email server?

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Another example of MX records affecting outbound email is improperly setup SPF records relying on the "mx" mechanism without any other mechanisms and not sending email from the MX IPs. –  Bort Feb 5 '13 at 19:34
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RFC 822 and RFC 2142 specifically require receiving mail as a condition of sending mail. Failing to comply with the rules will get you blacklisted. "RFC822 6.3, C.6 requires the presence of a <POSTMASTER@domain> mailbox name on all hosts that have an SMTP server." -- RFC 2142, section 1. –  David Schwartz Feb 5 '13 at 23:59
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3 Answers

up vote 3 down vote accepted

You are not required to have MX records just to send email.

However:

  • you must use a valid, existing and working email domain as sender address in all outgoing traffic (sending mail from something@nonexistentdomain.com is not allowed)
  • any domain used in email traffic can work without MX records if it has a valid A record, but this kind of setup is not much used on the 'net nor really encouraged. If a domain must be able to receive mail, set up valid MX records.
  • any domain used in email traffic (such as the sender address of the previous items) must have a valid and working postmaster@ account, that means the domain must be able to receive mail, that means the domain should have MX records

Short story: you don't have to have/manage MX records, but be sure to use a working email address as sender and be sure it is on a working domain with valid MX records.

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thanks very much for the brief answer! And what if the outbound smtp server is different from the inbound one? I mean I'm using Google Apps right now to send/receive emails, and the MX records are already set up. What If I'm using both? Is that a bad idea? –  CIRK Feb 5 '13 at 19:30
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No, it's perfectly normal for outgoing and ingoing servers to be different. Many many big shops actually have multiple incoming MX and different, multiple, SMTP-out servers –  Luke404 Feb 5 '13 at 23:13
    
thanks! And how can I set up the MX record in a way that they don't interfere with each other? Also how can I set multiple SPF records? –  CIRK Feb 5 '13 at 23:27
    
I'm getting this message from my domain manager: Caution: The main domain name (www.)mydomain.com is using MX : mail.mydomain.com already. If you want to add Google Apps, you need create a subdomain, e.g. xyz.mydomain.com or remove MX : mail.mydomain.com. –  CIRK Feb 5 '13 at 23:31
    
I actually asked another question regarding this at serverfault.com/questions/475847/… –  CIRK Feb 6 '13 at 0:12
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No, MX records are not used when sending outbound mail.

However, some mail servers may require that the domain of the from address have the necessary DNS records to support incoming mail, in which case you need either an MX or A record on that domain.

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Thanks! Is this to validate the origin of the from email? –  CIRK Feb 5 '13 at 19:09
    
@CIRK It's validation that the from address is vaguely valid. –  mgorven Feb 5 '13 at 19:21
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Just to send email you do not have to establish MX records for your own domain.

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