Hi @Kurt Stichelmans ,
Thanks for your reply.
According to my tests, I could reproduce your case when I performed the same tests on Outlook 2013 and Outlook 2019(password prompt once in Outlook 2013, and it would prompt every send/receive session in Outlook 2019) .
In my opinion, it may be designed to verify your credentials for each send/receive session to confirm the security of your account in Outlook 2019. And sorry for I couldn't find the relavant option that could change it.
In this case, as a workaround, we could try to check the "remember password" option and work with pst password only as I mentioned above, so that we could prompt the password window once in a session.