SMTP server hostname (e.g. "smtp.mail.me.com")
SMTP server port (e.g. 465 for TLS, 587 for STARTTLS)
Whether to use implicit TLS (true for port 465)
Whether to upgrade to TLS via STARTTLS (true for port 587)
SMTP username (typically the email address)
SMTP password (app-specific password for Apple)
Credentials and server info for connecting to an SMTP server.