It could be used uninitialized in case the call to
camel_ews_store_connected() failed, which can either when the store
is in the offline mode or the connection to the server fails.

Use the Mailbox address as the main email address and merge it with
the email addresses from the Contact element.

Similar to libsoup, also evolution-ews checks /usr/bin/ntlm_auth
whether a password is required, while this test "fails" and it
looks like the password is never needed. Even the connection fails
later, the code didn't try to ask for the password, but it should.

It looks like the priv::cancellable can be read/write without
thread safety, which can lead to a crash, as reported downstream at:
https://bugzilla.redhat.com/show_bug.cgi?id=1321119