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When I use command telnet <myhost.com> 25
from my home PC running Windows 7 it does not connect with message "Could not open connection to the host, on port 25: Connect failed." On the 587 port on the other hand connection works fine.
From my computer at work I can run telnet <myhost.com> 25
just fine.
I'm guessing that I've misconfigured my home workstation somehow.
How can I diagnose what is preventing me from connectiong to my SMTP server from home?
Than how a mail client is able to connect to a SMTP server if I can't telnet to it? – sebastian_t – 2017-02-24T23:03:27.073
1Are you sure your mail client is able to connect from within your network, and that it is using port 25? Anything using exchange would be going over http(s), receiving mail is either through pop/imap. Only stuff you send, that is not going through the alternate submission port would use port 25. – Zoredache – 2017-02-24T23:06:18.580
The use of port 25 is commonly restricted to reduce the ability of botnets and other spammers. Are you trying to connect to your work SMTP server on port 25, if so you may also be battling against the company firewalls (they're letting office PCs in but not internet PCs). Are you trying to get to a well-known public SMTP server, if so it is most likely what Zoredache said and your ISP is preventing outbound connection on 25 as part of their network-protection-safety; a call to your ISP's tech support would answer that (ATT does this, for example) – Ruscal – 2017-02-24T23:59:30.457