I cannot send e-mail (the test feature works, though).

[Guest]

My accounts receive e-mails, and test okay, but when I try to send out an
e-mail, I get the following code:

"553 sorry, that domain isn't allowed to be relayed thru this MTA (#5.7.1)"

 

[Jeff Stephenson [MSFT]]

You need to set up to authenticate to your outgoing server. Do so on the
"Outgoing server" tab of your account dialog.