Some SMTP servers have special requirements. The following variables implement support for common requirements.
smtpmail-local-domain controls the hostname sent
in the first
HELO command sent to the server.
It should be set only if the
system-name function returns a
name that isn’t accepted by the server. Do not set this variable
unless your server complains.
smtpmail-sendto-domain makes the SMTP library
add ‘@’ and the specified value to recipients specified in the
message when they are sent using the
RCPT TO command. Some
configurations of sendmail requires this behavior. Don’t bother to
set this unless you have get an error like:
Sending failed; SMTP protocol error
when sending mail, and the debug buffer (see Debugging)) contains an error such as:
RCPT TO: someone 501 someone: recipient address must contain a domain