WebMail Works But SMTP Says Sender address rejected: not owned by user and I've tried EVERYTHING please help

MailInABox on Ubuntu 18.04
I have tried the main email address as SMTP login and as recipient
I have tried aliases I have tried everything over and over but all I get is the same error “Sender address rejected: not owned by user”
Will you please help me finally resolve this issue? I would sincerely appreciate it so much.
I installed MailInABox three times a few years ago on Ubuntu 14.04 and never had one problem. I wish that version was still available :frowning:
Please help
Jeff Brown

Please describe what you are attempting to send from and the settings of that app. @BuddysMasterJeff

Also a screen shot of your aliases page would help … feel free to PM here (you are limited as a new user) or to reach out on Slack.