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SMTP/port 25 blocked

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SMTP/port 25 blocked

I was testing my SMTP server from an external machine and can't telnet to port 25 -- it just times out.
I can still receive mail though, which is a bit weird.
If I set my router to forward port 1025 to 25 on the mail server, then telnetting to the SMTP server works.

Is PlusNet blocking telnet requests on port 25?
How do they distinguish between telnet and a MTA?

(I realise I also need to ask this question about the network at the other end too)
4 REPLIES
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SMTP/port 25 blocked

PlusNet do not block port 25.

Can I ask where you are attempting to make the test connections from?

Some ISPs block outbound port 25 attempts, to prevent people running there own mail servers.
Community Veteran
Posts: 14,469
Registered: 30-07-2007

SMTP/port 25 blocked

Quote
How do they distinguish between telnet and a MTA?


It does not and cannot distringuish what is connecting to it. Telnet is one of the ways in which SMTP servers can be tested as described in the tutorial Servers: Telnet as a Diagnostic Aid.

What server were you telneting in to or trying to connect to on port 25?

Was this from a plusnet ADSL/dialup connection - i.e. from a system already on plusnets network?
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SMTP/port 25 blocked

I was telnetting from bris.ac.uk to my PlusNet machine, so perhaps it is something there.

Thanks anyway.
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SMTP/port 25 blocked

hehe i am from bristol - that'll be that dodgy uni we got - that's what you get for building it at the top of beer mile - er i mean Park Street Wink

How can plusnet block port 25 and offer a relay SMTP?