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Cannot connect to SMTP service from a POP3 Outlook account


We had an announcement from one of our customers this morning that they have changed their ISP.

They access email externally using POP3.

We lock down both SMTP and POP3 by IP address.

They supplied us with the new IP address and I have added this to the Connection Control on the POP3 Virtual Server and I have added it to the Relay and Connection Control on the SMTP Virtual Server.

I've then restarted both services.

However, they can only receive email and not send.  

When testing the account settings, POP3 authenticates correctly, but it then fails to send the test message because it cannot connect to the SMTP service.

Have I missed anything?  

I have tested the account on a device that connects via an already added IP address and it works as expected.

I'm really rather confused and I'm hoping I've just forgotten to add the IP address to somewhere else.

Any help would be most appreciated.
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1 Solution
Hi Xperta,

Your customers new ISP is probably blocking port 25, try to use a secure connection. Or to troubleshoot this map port 26 (public) to port 25 (internal) and verify.

Hope this helps.
XpertaAuthor Commented:
You know what, I fired off an email to the site (at the same time as opening this question) asking them if there are any port 25 restrictions and they have just had response from their ISP stating there are.

Fairly sure that will be the problem then.

Thanks for the response
Glad to have helped :)

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