We have several use cases for 3rd-party SMTP including outgoing encryption, archiving, and insertion of T's&C's.
As you probably discovered, the cc or bcc to every email does not meet needs for archiving, so we have implemented SMTP to allow the server to not only forward the Email on, but to also copy to a specific folder.
We have customers that want to ensure an info footer is applied to every outbound email without agent intervention. The auto signature feature helps but does not meet the 100% objective. The SMTP server was able to insert this paragraph after the agent sends.
As for authorization, that has been a moving target as Genesys continues to support different methods. It was a real pain when Microsoft announced deprecation of one method and introduction of a newer method with very overlap time. Genesys came through eventually and Microsoft delayed the deprecation.
IMAP helps us on the inbound to give us more variety of how emails get into Genesys and we are looking forward to the Q1 release of the Microsoft Graph API integration to allow even more controls and transports.
@Jody Nabuurs, do you have a comment on this?