There is no user interface to change the outgoing method of an IMAP account.
If you used Sendmail so far but now want to use an SMTP connection instead:
Close
Find and open the corresponding account file in
In the [Mail Transport]
section, replace
BackendName=sendmail
with BackendName=smtp
or vice versa.
Restart the evolution-source-registry
background
process, for example by rebooting your system.
Start