Is it possible to use a SRV rule on my DNS to receive mail on port 2525 instead of port 25 ? If it is possible how can I setup this rule correctly ?
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No.
The MX mechanism does not grant the ability to provide mail service on alternative port numbers @wikipedia
filimonic
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Ok then i am gonna use a tcp proxy – user2663781 Jan 31 '15 at 11:52
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On a purely theoretical level it would be possible to do so using SRV records but what prevents this from being applicable to your problem is that MTAs only make use of MX and address records (A/AAAA). Ie, in practice no one would look up your SRV record if you added one.
In effect SRV can be seen as a generalised and extended version of the MX record type and it would be greatly beneficial if it was used with more protocols. Unfortunately it was introduced too late to be a factor in the specification of many major protocols that have been around for a long time (HTTP is probably the archetypical example of this, SMTP not as much as it at least has its own specialised MX record type which solves most of the same problems).
Håkan Lindqvist
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