In message <[EMAIL PROTECTED]>, Todd Vierling writes:
>
>The default recommendation I give anyone these days is to use no
>secondaries, and let the sender's mail server queue it up, as that's the
>fastest implementation path. As a second stage, and only if the expertise
>and time is available, then a backup MX with some sort of recipient
>validation at SMTP time can be implemented.
>
The usual justification for a secondary MX is when the MX servers have
some sort of special access to the ultimate recipients -- non-SMTP mail
delivery, firewalls that they are privileged to pass, etc.
--Steven M. Bellovin, http://www.cs.columbia.edu/~smb
