Thus spake "Shaun Bryant" <sbryant@ThePit.org>
I am currently working on a high volume mail project. The question came up whether or not the run Cisco's SMTP fixup protocol. I am looking for any experiences good or bad.
Last time I looked, the "mail guard" feature replaces EHLO messages with NOOP (among other things). Some ESMTP-capable mailers figure out what's going on and retry with HELO, but others get confused and end up bouncing all mail going through that path. I don't know who decided EHLO is not a "safe" command, but (a) it's been standard for many, many years, and (b) replacing it with NOOP does not have a "safe" effect. Do not use this feature if you value mail reliability.
Please respond off list
Actually, this is far more on-topic than most NANOG drivel, so I'll respond here :) S