I'm not really an EWS user, just trying to help debug a mailing application that stopped working last year.
We get an error message when trying to send() that the connection was forcibly closed. Reading up on the issue it seems like a lot of folks are saying it's a TLS version problem.
Someone here think it's because we are using Basic Authentication (instead of Modern Authentication with OAuth 2.0). We don't see any issues directly related to authentication.
By still using Basic Authentication, can that cause the connection closed issue when we try to execute the send() method?
No a connection being forcibly closed is most likely either TLS, bad ip reputation (eg a lot of spam/fraud coming from a certain IP that has been blacklisted) or your sending a message with a very large attachment in a single request. If it was a Basic Authentication disabled issue you would get a 401 error, if its was that EWS had been disabled (eg via set-casMailbox) you could get a 403.