Mail Delivery Attempts despite nonexistent MX Record

[haiberg]

Hello,

This might be a silly question: Is there an option in Proxmox to immediately send an "Undelivered Mail" notification if no MX record exists for a domain?

I did some tests regarding this issue. If a domain is not registered, the undelivered mail notification is sent back immediately. However, if the domain has an A-Record but no MX-Record, Proxmox continues trying to deliver the email for several days until an "Undelivered Mail" notification is eventually sent.

In the queue, such messages appear with an error like: No route to host.

As example, you can use user@testdom.com. This domain testdom.com exists and has an A-Record but no MX-Record.
Thank you!

PS: In the Relaying Options the setting for "Disable MX lookup" is enabled, but this has the reason (if i remember correctly), that otherwise the transport to the internal mail server won't work properly.

 

[Stoiko Ivanov]

I did some tests regarding this issue. If a domain is not registered, the undelivered mail notification is sent back immediately. However, if the domain has an A-Record but no MX-Record, Proxmox continues trying to deliver the email for several days until an "Undelivered Mail" notification is eventually sent.

This is the normal behavior in case there is no MX-Record delivery is tried to the "host" (A/AAAA/CNAME record)
https://en.wikipedia.org/wiki/MX_record#Fallback_to_the_address_record

 

[haiberg]

Thanks for the feedback.

Would it be a possible new feature for proxmox to do a separate the maximal_queue_lifetime for destinations that have a MX and ones who doesn't?
For us I would set the maximal_queue_lifetime for nonMX Domain to 12 or 24h where I would keep the 5 day for ones that have a MX.

So that email address typos where the domain "unfortunately" exist but isn't mailing (because of no MX record), get earlier a Undelivered Mail
Or is this a dumb idea

 

[Stoiko Ivanov]

There are quite a lot of domains, and hosts that do receive mail directly and have no need for an MX record or would benefit from having one pointing to themselves in any way.

in my experience it really is not that uncommon - and it's also something that has been around for as long as emails have existed (that errors in sending mails are only reported after a while (with the while being between directly and up to 5 days (however most mailservers that queue mail, and run into temporary delivery issues (4xx responses from the next server, or connection timeouts, do send informational messages that the mails is still queued after a few hours)