Unable to send emails - relay.plus.net refusing connection

[#1]

My POP3 account on Outlook 2016 32-bit edition, suddenly stopped sending e-mails, but could still receive.

I deleted the account and tried to set it up using the info at https://www.plus.net/help/email-guides/how-to-set-up-plusnet-email/ with the additional info: "If you've been with us a while, your domain might be '.force9.co.uk or '.free-online.net'. If so, change '.plus.net' to '.force9.net' or '.free-online.net' for both your incoming and outgoing servers."

Repeated combinations of parameter settings allow the incoming test to pass but the outgoing (relay.force9.net) to fail.  One of the latest errors was:

"Send test email message: Your server does not support the connection encryption type you have specified. Try changing the encryption method. Contact your mail server administrator or Internet service provider (ISP) for additional assistance."

I am appealing to the community for help, since the two chat sessions with PlusNet employees result only in their smug assertion that the error does not lie with them, so they are unwilling to help me move forward.

[#2 · Accepted solution]

I believe that Outlook assumes that the outgoing Email server at Plusnet's end will, like the most of the world, be encrypted. Plusnet's are still in the last century and unencrypted. You need to set the outgoing port in Outlook to 587 or 25. See 'what other settings do I need' here. https://www.plus.net/help/email-guides/how-to-set-up-plusnet-email/

[#3]

It is not just a matter of setting the port (should be 587) but also ensuring encryption has not been presumed (set it to none).

I would guess that some software update changed the setting!!!

[#4]

That solved the problem!

Many thanks for the timeous response