Email just won't send to a specific domain.

TcNobo · Sep 5, 2022

I’ve fixed all the issues I’ve had with Mailcow, but one has stuck. I can’t email one specific domain. Every other email sends just fine.
I ALWAYS get the following in Postfix’s log: to=<user@address.co.za>, relay=none, delay=15450, delays=15450/0.02/0/0, dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for name=address.co.za type=MX: Host not found, try again)
and an email that bounces back.

But if I look up using MxToolbox, the address has a valid MX record.

What can I do? I’ve heard of setting postfixes DNS, and tried using docker exec -ti mailcowdockerized-postfix-mailcow-1 and entering nameserver 8.8.8.8 into /var/spool/postfix/etc/resolv.conf, but this hasn’t done anything.
I’ve deleted the file in the meanwhile just incase it does something unexpected.

Running dig address.co.za MX returns the correct question, answer and additional sections as expected…
Running the above inside the container just hangs there forever… Then times out.

Any help?

TcNobo · Sep 5, 2022

I assume I JUST ran out of time while editing the post.

As a temporary fix (I do hope this is okay) I’ve added the IPv4 and IPv6 DNS addresses of my system, in this case Hetzner’s DNS, as a new item right after dns: - ${IPV4_NETWORK:-172.22.1}.254. Now the mail sends.
I assume this would also have fixed my other post? HFILTER_HOSTNAME_UNKNOWN

mailcow communityDiscussion

HFILTER_HOSTNAME_UNKNOWN for almost all mail

TcNobo

Hey. I’m relatively new to Mailcow. I’ve got a Hetzner VPS with IPv6. Oddly, even after reinstalling Debian and switching to Ubuntu… I’ve still always received “HFILTER_HOSTNAME_UNKNOWN” as a reason to bounce almost all emails. Most of which comes from IPv6 addresses and says something about

1 1 Aug 18, 2022

. Can’t test this as another email hasn’t had issues like this recently.