Routing bounce and watchdog mails

ecdlguy

Hi,
At our university, we have to use a relayhost for our local departement mailserver.
I’m using sender dependent transport maps for our maildomain as described in the docs and this works as expected.

However, since bounce and watchdog mails are send from MAILCOW_HOSTNAME , they don’t get delivered because our mailserver cannot directly talk to other mailservers. I tried different approaches to make this work:

Add a maildomain MAILCOW_HOSTNAME but this is not allowed.
Create a transport map * -> smarthost. This leads to a mail loop for mails coming from external senders
Create a transport map for everything except the configured maildomain, like !/maildomain$/. However I cannot enter this in the gui (Destination format “/localhost$/” is invalid)

I’m sure there’s a much simpler solution…

cheers, Thorsten

esackbauer

Watchdog emails will always use the MX and direct connection, as explained here:
https://docs.mailcow.email/post_installation/firststeps-authorize_watchdog_and_bounces/

Regarding bounces I have not yet tested it via sender dependent transport. You still need to setup SPF and DMARC accordingly for the mailcow hostname.

ecdlguy

Thanks.

Using a sender dependent transport would require changes to Postfix config files, because it’s not possible to create a maildomain with MAILCOW_HOSTNAME in the webinterface. Or am I missing something?

What do you think about the idea of using a global transport map like I wrote in my previous post?

Create a transport map for everything except the configured maildomain, like !/maildomain$/. However I cannot enter this in the gui (Destination format “/localhost$/” is invalid)

However, I don’t understand my regex is not accepted, because the input mask in the webinterface suggests it should:

Or could this be somehow accomplished using Sieve?

Regarding the watchdog this was my understanding to so thanks for confirming this.

esackbauer

I guess the easier solution for your case is using no sender dependent transports at all, and put a relayhost config line into the postfix configuration.
https://www.postfix.org/postconf.5.html#relayhost

ecdlguy

Ok I see. Uff. So using a smarthost with mailcow is a bit painful 🙁
Hopefully using a relayhost config line does not have other side-effects?
Is it possible to change / rewrite the sender address of the bounce mails?

esackbauer

ecdlguy So using a smarthost with mailcow is a bit painful 🙁

Only in your case 😉
Mailcow was designed to run on its own, and being able to send mails directly to external mail servers, to have as few as possible MTAs inbetween which could be possibly harvesting/analyzing the mails in transit.

ecdlguy Is it possible to change / rewrite the sender address of the bounce mails?

Not that I am aware of.

ecdlguy

Mailcow was designed to run on its own, and being able to send mails directly to external mail servers, to have as few as possible MTAs inbetween which could be possibly harvesting/analyzing the mails in transit.

In our case it’s even worse, we have the following chain:

(in) DFN mailgateway -> university mailgateway -> mailcow -> university mailgateway -> DFN mailgateway (out)

However, I could imagine that this is often a problem…?

Would it be possible to use a global transport like this:

This would relay mails for my domain to localhost (maybe relay:localhost has the same effect as just local?)
What do you think?
Thanks again for your support, I really appreciate.

esackbauer

I don’t think that will work, because it covers only intentionally sent mails from users.
Not the special case of bounce emails, this could maybe only be covered by postfix tweaking. With watchdog mails you are probaly totally out of luck, because it is sent directly from within the watchdog container, bypassing postfix. Which is the whole point in that specific case.
I would suggest you discuss this with support team of mailcow (Tinc GmbH).

ecdlguy

For the watchdog I plan using a webhook.