||Once, at the start of each SMTP connection.
||Do nothing; return SMFIS_CONTINUE.
||the opaque context structure.
||the host name of the message sender, as determined by a
reverse lookup on the host address.
If the reverse lookup fails
or if none of the IP addresses of the resolved host name
matches the original IP address,
hostname will contain the message sender's IP
address enclosed in square brackets (e.g. `[a.b.c.d]').
If the SMTP connection is made via stdin the value is
||the host address,
as determined by a |
getpeername(2) call on the SMTP socket.
NULL if the type is not supported in the current version or if
the SMTP connection is made via stdin.
||If an earlier filter rejects the connection in its xxfi_connect()
routine, this filter's xxfi_connect() will not be called.