Email servers can receive emails for local users (those with addresses in that domain) or "relay" them on to other mail servers. To limit spam, mail servers are generally configured to only relay mail from known users or machines. As a result, most mail servers require a login for authentication, which requires MailCall to know the login account and password to use.
This information can be defined in mailcall.ini (login=x and password=y lines) or in the mailcall template variables x.login$ and x.password$. If a mail server requests authentication, MailCall can then provide it. MailCall supports the AUTH LOGIN authentication method. Authentication requires Mailcall 2.0.