Log in on an SMTP server that requires authentication.
The arguments are:
- user: The user name to authenticate with.
- password: The password for the authentication.
Keyword arguments:
- initial_response_ok: Allow sending the RFC 4954 initial-response
to the AUTH command, if the authentication methods supports it.
If there has been no previous EHLO or HELO command this session, this
method tries ESMTP EHLO first.
This method will return normally if the authentication was successful.
This method may raise the following exceptions:
SMTPHeloError The server didn't reply properly to
the helo greeting.
SMTPAuthenticationError The server didn't accept the username/
password combination.
SMTPNotSupportedError The AUTH command is not supported by the
server.
SMTPException No suitable authentication method was
found.