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sinsi avatar Server

Internal email server using non-standard ports

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sinsi

Our backup server is a Ubuntu box at the boss's house which has a static IP address from the ISP (Optus) but they block the usual email ports - I have no issue with this, it's well known. Can I configure the server and client to use a different port e.g. SSL on port 50332. It would be restricted to the domain (no sending to or receiving from other domains).

I'm just after a yes/no answer, not details on how to do it if it is possible (it's no fun being spoon-fed). To me, logically it is feasable but my knowledge of email servers is limited to setting an original server up with DMARC/DKIM/SPF (and then having it blocked two months later)

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FatRabbit avatar Server
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FatRabbit

You need to open your /etc/postfix/master.cf on your server and spawn a smtpd daemon with a different port.

One thing you should know: The first column of this file is the port number OR the name attributed to this port as per /etc/services i.e: if the line begins with smtp, it means the corresponding daemon will listen on port 25 (as indicated in /etc/services)

You could for example spawn one daemon to a different port by editing this first column as long as there is no conflict.

An example of a smtpd daemon listening on port 10025 instead of 25 for incoming e-mails:

10025       inet  n       -       y       -       -       smtpd

You can leave the one listening on port 25 (smtp) since there is no conflict between the two.

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sinsi avatar
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sinsi
Exactly what I needed, cheers!
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Bob

You can configure your own systems and services to run on any port, but when you want to use this server as a back-up mail server, a secondary MX record to cache incoming e-mail when your primary mail server is down, that won't work.

SMTP traffic between e-mail servers on the internet can use non-standard ports, but only when explicitly configured to do so by both the sender and the recipient. As a recipient you can't say: please send my e-mail to TCP port 52525 of the server mx2.example.com instead of the default TCP port for SMTP, port 25 and reliably expect all senders too honour that.

Unfortunately configured otherwise senders will always use the default port, TCP port 25 for SMTP.

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sinsi avatar
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sinsi
This will be strictly used within the local domain, no outside emails so no other servers. It's basically a quick way to message each other from different sites across the city. I did want to use .net to query the server from the main work program otherwise I would look into a messaging set up.
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