Trouble Receiving Emails Sent via Submission Port in Mailcow

MickoLjudinicko

Hello!

I’m experiencing issues with receiving emails on my Mailcow setup. While I can send emails without any problems, receiving them is a challenge. Currently, only mailboxes within the same domain can exchange emails. External sources, like Gmail, can’t send emails to my setup.

It’s worth noting that my ISP has imposed significant traffic restrictions. Both SMTP and SMTPS are blocked, and they’ve refused to make exceptions. However, both IMAP and IMAPS are active, accessible from external sources, and are not blocked by the ISP. As a result, I’m unable to modify my rDNS record, though I’m not sure if that’s relevant to my current issue.

The only port I’ve been permitted to use is the SUBMISSION port (587). I’ve attempted to diagnose the issue using custom Python scripts to send emails from external sources. However, in every case, the Mail Delivery System reports a failure in sending the email.

Any insights or solutions would be greatly appreciated. Thank you!

DocFraggle

And you are sure that your ISP allows connections to port 587? Did you check this with an online tool like https://mxtoolbox.com/SuperTool.aspx?

On the site mentioned above you can select “TCP lookup” from the dropdown menu and enter your mailcow DNS FQDN or IP with port 587, like this:

your.mailcow.fqdn:587
or
1.2.3.4:587

It should look like this:

accolon

You won’t be able to receive mails from external sources without port 25. Communication between mail servers generally uses the SMTP port.

MickoLjudinicko

Thanks for your quick replies!

@DocFraggle Thanks for the advice, I’ve checked it with this tool, another pen-testing tool as well to lookout for the SUBMISSION port and in both scenarios the SUBMISSION port was reachable from outside.

@accolon That’s a true bummer. I’ve read online, that relay services from amazon or setting up a VPN tunnel to another server, and redirecting the SMTP traffic from the VPN endpoint might work to overcome this ISP blockage issue, but unfortunately all of these methods cost too much in contrast to what I have. I don’t send many emails, it’s not for business use.

Any ideas or advice to get over this?

Any insights or solutions would be greatly appreciated. Thank you up until now!