In MABS, you can setup an SMTP server for sending emails. The issue is that there is a requirement that the username you supply in the SMTP username field must be a domain user. I have no idea why this is required, but it makes using a 3rd party service such as SendGrid as your SMTP server much harder. In Sendgrid, I setup an API Key which then says I must supply the username as "apikey" and the password is the actual apikey.

Obviously, the user "apikey" does not exist in the domain, so when MABS checks this, it fails.

I don't see why there is a check to see if the user exists in the domain when setting up an SMTP server.