5.7.1 Authentication is required

Sounds like you do not have something right in your SMTP settings.

From the Menu Bar select Tools-Account Settings-Outgoing Server (SMTP) and double check what you are supposed to have. Outgoing Server is at the bottom of the account listing on the left side.

No menu bar? Press the alt key.

Ahhhh, you helped me find the outgoing server setting a few weeks back. I changed the pop and smtp server paths and changed the ports as well. The pop settings are under each account, however it appears the smtp setting and new port setting are set just once for all 3 accounts. I can send fine from my main account but when I try to send from the subs I get a message that it is sending from the correct smtp path, but then I get the error telling me that I'm trying to send from account name: res10nqja@verizon.net. That is not even close to any of my account names.

To Airmail: I finally figured it out... I had to add 2 more servers - one for each account - and specify the sender name and set it as the default. It took some finagling because it appears that you have set the same default for all 3 accounts. Once I ignored that I found that I can send successfully between all 3 accounts. Thank you once again for putting up with a novice!

Sorry I slept in this morning. ☺ Glad you got it figured out. Yes you need, or should have, an SMTP server specified for each account.