Unable to setup Emails to be sent from SuiteCRM

Hi,

I am using Version 7.6.4. I have setup a mail account called it1@mydomain.com for sending out emails using SMTP. I am able to send emails from the User β€œit” which is linked to it1@storkrubber.com but for all other IDs it gives error - Sender address rejected, not owned by user it1@mydomain.com. I have ticked Allow users to use this account for outgoing email. Is this an issue at SuiteCRM end or mail setting issue. It seems to work using IDs on another domain which I have access to but not on the production server domain.

Regards
Amal