Each employee gets their own email: personal SMTP for outgoing & IMAP/POP for incoming mail in Odoo.
Configure different outgoing mail server for each user
Add outgoing mail server for specific user.
Outgoing Mail Server by User SMTP server by user based outgoing mail server per user based SMTP server per user wise mail server user wise smtp servers per user outgoing mail servers per user outgoing mail server by company smtp server by company