SMTP problem on BTinternet, mail not sending

Hi, For the last week I have been having problems with my SMTP server connected to BTinternet. When I send a message it just sits there in my Outbox! The settings I have been using have been fine for the last 18 months without problems. The current port setting is 25, but I have tried changing that to 465, but the problem remains. I have used the diagnostic tool in “Accounts”, but it says it can’t fix the problem. I am sure this is an Em Client issue, as I have other client software, running POP3/SMTP, using the same settings running on other devices, for the same email address, without problem. Also, to get over this problem (hopefully temporarily), I configured Windows Live mail on the same PC with the same settings, and it runs without any problems. Any solutions for Em Client?

I have now resolved the problem myself by deleting the account and recreating it!  Why it occurred in the first place and on on two different computers at the same time I still do not understand!