can't send mail in Kmail

[OldSmoky2]

Hi... I decided to make the switch to KMail from Thunderbird (I'm using 14.04). It detected my account settings and receives mail but I can't send mail. When I try, I get an error message: "Failed to transport message. The server did not accept the sender address "(my name)@gary-inspiron-660". The server responded: "Syntax error in arguments".
So I've looked around a bit trying to figure out how to correctly set the domain. Under settings/configure kmail/ accounts/sending, my default domain is indeed set to gary-inspiron-660. I assume it should be set to something having to do with my email account, which is AT&T. But I can't find much documentation on exactly what to do to fix it. Any ideas?

[OldSmoky2]

OK, well, that was fast. I kept looking around and found the answer in a 10-year-old thread at Linux Questions. I just changed the default domain to "att.net" and it sends now.

[SteveRiley]

When configuring an email sending (outgoing) account that requires authentication, you have to supply the email address and password associated with the account at the provider. In nearly every instance that I can imagine, this will be the same email address and password that you use for configuring an email receiving (incoming) account.