Hi all,
I noticed a strange issue and I can’t find the source.
I have a straightforward mailcow deploy and been running this for a couple of years now rock solild!
Last week I wanted to reply to a email I received lets say from domain a.org.
After some time I got an email from my mailcow install stating it isn’t able to deliver it but, loyal as it is, will keep trying.
Now the message retry period is passed and so it notifies me it was unable to deliver the message.
So now I decided to do some detective work. I noticed the error is
(Host or domain name not found. Name service error for name=a.org type=MX: Host not found, try again)
So I tried a dig executed inside the postfix container for the host sudo docker exec mailcowdockerized-postfix-mailcow-1 dig a.org MX and got a
WARNING: recursion requested but not available
and an empty reply. So executed the same command for a couple of different domains to see what this would do.
So running the command again sudo docker exec mailcowdockerized-postfix-mailcow-1 dig google.com MX and behold it gave a valid reply
google.com. 300 IN MX 10 smtp.google.com.
so tried a couple of others (i.e. microsoft.com; facebook.com etc) no issues here all valid reply’s.
So for some reason resolving a.org wont play.
Next I tried the dig command on the docker host itself this one query’s a local DNS server running pihole and unbound. And behold no issue in querying here dig a.org MX gives a valid response and no warning about the recursion.
So for this specific domain there is an issue querying the MX record from unbound and as a result isn’t able to deliver the email.
The other way around is also interesting as this morning I received a phone call from the a.org organization stating they are unable to reach out to me via email. I suspect the issue here is that my mailcow instance is denying the delivery because it isn’t able to resolve the sender ip (not sure though since I didn’t see the error and wasn’t able to find anything on my side).
Just to be clear all other outgoing and incoming emails are flowing just fine and a query inside loki/grafana viewing the last 7 days show no other domains with this issue only errors like:
Warning: dnsblog_query: lookup error for DNS query 227.56.143.149.bl.ipv6.spameatingmonkey.net: Host or domain name not found, try again
warning: dnsblog_query: lookup error for DNS query 227.56.143.149.b.barracudacentral.org: Host or domain name not found. Name service error for name=227.56.143.149.b.barracudacentral.org type=A: Host not found, try again
Any thoughts/hints that might point me in the right direction would be appreciated.
Thank you!
