After installing Office 365 this error started happening. I cannot send any emails. I had Outlook 2010 installed before.
I edit the Account Settings area and click Change Account, the Test Account Settings button works fine. I have 2 email accounts using separate POP3/SMTP server connections and both work fine in the Test Account Settings. When sending an email the Send/Receive Error message still appears.
This is not an issue with the POP3/SMTP settings, in my opinion, if the test settings works correctly. The test message does get sent (verified through a web interface for the email).
What can I do next? My Outlook client is pretty useless if I can't send an email.