POP3 - new industry wide changes one has to assume. Some people report problems when sending. I know of three personally, and there are many on forums reporting problems. People who haven't changed anything.

My solution is there for anyone who has seen this problem. Probably where SMTP uses a different URL from POP3 receive. FWIW IMAP uses the same URL. If you haven't got the problem you won't see the need for a solution.

Given that support at my ISP can't tell me that there is a problem, can't see what I do wrong on POP3, then tell me I can't send e-mails from Outlook, period. And don't suggest IMAP. I would bet Thunderbird will show the same problem from the same PC. It must have taken the industry by surprise. It is probably a Microsoft/Linux update that is very subtle.