I have a similar issue. Regardless of what I set in the FROM field, AcyMailing uses the address that was imported from Joomla initially. I have changed the email info for Joomla and can send mail from there, but this had no impact on the FROM address in AcyMailing. Does anyone have an answer? I've marked the email address initially imported from Joomla as OLD_EMAIL in the error message:
Error sending message Test e-mail from http://my.site/ to OLD_EMAIL
The following From address failed: OLD_EMAIL : MAIL FROM command failed,Requested action not taken: mailbox unavailable
Sender address is not allowed.
,550,SMTP server error: MAIL FROM command failed Detail: Requested action not taken: mailbox unavailable
Sender address is not allowed.
SMTP code: 550SMTP server error: MAIL FROM command failed Detail: Requested action not taken: mailbox unavailable
Sender address is not allowed.
SMTP code: 550
2019-10-28 23:09:01 CLIENT -> SERVER: EHLO my.site
2019-10-28 23:09:02 CLIENT -> SERVER: AUTH LOGIN
2019-10-28 23:09:02 CLIENT -> SERVER: <credentials hidden>
2019-10-28 23:09:02 CLIENT -> SERVER: <credentials hidden>
2019-10-28 23:09:02 CLIENT -> SERVER: MAIL FROM:<OLD_EMAIL>
2019-10-28 23:09:02 SMTP ERROR: MAIL FROM command failed: 550-Requested action not taken: mailbox unavailable550 Sender address is not allowed.