Support for Authentication to relayhost

[tiberios1]

Is your feature request related to a problem? Please describe.
My relayhost now requires me to pass my username and an app password before relaying my outbound messages.
5.1.0 Authentication Required (VM401) (in reply to MAIL FROM command)

Describe the solution you'd like
The ability to pass a username and password to the relayhost

Describe alternatives you've considered
I could change my relayhost, but I'd prefer not to.

Additional context
Add any other context or screenshots about the feature request here.

[jeboehm]

Fixed in #204