External SMTP Timeout with VPS Email Server and Separate DNS

Virtualmin
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SYSTEM INFORMATION
OS type and version Ubuntu 22.04 LTS
Webmin version 2.402
Virtualmin version 7.30.8
Webserver version Apache version 2.4.52

Hello everyone,

I am running an email server on a Virtualmin VPS for my domain, but the public DNS is managed separately. All MX, A, SPF, and DKIM records are configured, but DMARC is not yet set up. External SMTP tests always time out, and emails from external servers cannot reach my VPS. How can I properly synchronize the public DNS with my VPS and configure DMARC so that emails are delivered correctly?
I would appreciate your help.

2

Does your provider block port 25? Many do by default.

2 Likes
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If you see all timeouts, you do not have port 25, and thus don’t have a mail server.

You could test from the server:

telnet mail.virtualmin.com 25

And, you’ll also need to test incoming from another system.

1 Like
4

Thanks for the suggestion. I’ve tried telnet mail.virtualmin.com 25 from outside, but it’s still timing out. I also tested it on MXToolBox and it failed. The VPS firewall is fine, so it seems like the issue is probably on the provider’s side. Could this be because I haven’t set up a Reverse DNS / PTR record yet? This helps other servers verify emails from the VPS and prevents them from being marked as spam.

5

Thanks for your advice and the documentation link. I’ve read through everything you shared, but the result is still the same — port 25 from outside is timing out. It seems like port 25 might be blocked by the provider. Could this be because I haven’t set up a Reverse DNS / PTR record yet? This helps other servers verify emails sent from the VPS so they don’t get marked as spam.

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Providers block it to prevent spam. If you are on an actual provider, they may open it for you. If this is a home server, probably not.

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Got it, thanks! I’ll reach out to my VPS provider to have port 25 opened.

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You don’t try that from outside. You try that from inside your server.

You try telnet yourserver.tld 25 from outside. But, the outside server needs to be one that also has port 25, which is not true of a lot of home internet services.

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No. Nothing at the network layer has anything to do with DNS/PTR.

Other servers might block you if you send email to them without reasonable DNS and SPF and maybe DKIM, especially if it looks spammy, but your hosting provider is blocking you regardless of all of that. You don’t have port 25, thus you don’t have a mail server. None of that other mail stuff matters unless/until you have port 25.

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