Company email blocked at premises but not elsewhere!

Have a client with 4 pop3 email accounts on their company domain hosted by a company called Intimation with BT-supplied broadband. Yesterday both their incoming and outgoing email stopped working with no changes made to their internal systems. Outlook Test Account Settings returns “Outlook cannot connect to your incoming email pop server.. error 0x800CCC0E”. Telnet <mail server’s ip address> 80 fails. So as if something firewall-related blocking port 80. But now for the weirdest bits: Setting up a test email account not attached to the company domain WORKS… and setting up one of their email accounts on a pc at another site WORKS. Taking a laptop with their email setup on it FAILS at their site but WORKS at external sites. Router has been replaced with a new one out-of-the-box (so no firewall rules) to no avail. As if their mail server is blocking their IP address for some reason (though this is denied by tech support). How odd is all this?!
laurencoullAsked:
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KimputerCommented:
Why is it port 80 ? POP3 uses 110
laurencoullAuthor Commented:
Gaaaaaah !  You can tell how much stress this has caused me today! OK 110 it is. Sorry all.
KimputerCommented:
Okay, if it's a typo, and you did use 110, then it's either a firewall or routing issue. However, this could be an issue at your side or their side, that makes it a bit difficult to analyze. Try some traceroutes as a next step.

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