SMTP Relay MX problem


I hope somebody can help me in regards of this topic.

I have configured the sending of emails via postfix over relay account definde within smtp_auth. Based on that I get error message with logfile The server checking in someway the mail record:

Jul 24 12:02:46 mail postfix/smtp[4489]: warning: no MX host for has a valid address record

Jul 24 12:02:46 mail postfix/smtp[4489]: warning: relayhost configuration problem

Jul 24 12:02:46 mail postfix/smtp[4490]: E62782FF266:, relay=none, delay=2369, delays=2369/0.11/0.01/0, dsn=4.3.5, status=deferred (Host or domain name not found. Name service error for type=A: Host not found)

Variable set to:


If I configure the mail sending via a different smtp server (test with strato) the server selects the mail relay host in right way an send mail out to other account:


Jul 24 12:15:47 mail postfix/smtp[6510]: 768803019B9: to=< >,[]:25, delay=0.74, delays=0.03/0.04/0.32/0.35, dsn=2.0.0, status=sent (250 2.0.0 OK

If I connecting outlook direct to the mail account I can send mails out to other addresses with Outlook by using the same smtp server ( but if I use the mail relay from Postfix I get such error record. Is it possible to prevent that the postfix checking the MX record?

It seems, that
does not allow forwarding of emails of a different domain as a mail-relay.
As you can see, neither a MX-record nor an A-record of does exist in the DNS. So mails will be rejected. It is a security-feature.
In the opposite Strato allows it, because they offer the mail-relay.

If also allows to be handled as mail-relay, you should have a look on their support pages, how to enable the relaying.

Hello Mornsgrans,
thx for your clarification! I will check the documentation. In case that I can’t find any solution in the documentation, would it be possible to setup the server in the same way like e.g. outlook send out mails via SMTP connection to prevent this behaviour?

It may be possible, but only aufter configuring as the user as on outlook and then only it will possible to send mails as the user (sender’s mail address) as the mail account is configured.

In my opinion you will need a separate mail gateway, which allows sending mails as different senders at a different vendor. - Since I use an own UCS-server, I use a mail-relay at for a small annual fee.