Re: OT? /dev/null 5.1.1 email

["Steven M. Bellovin" <smb () cs columbia edu>]

In message <Pine.WNT.4.63.0507052219510.5600@jvc>, 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