[quote user="Brian Fluet"]Have since discovered that the recipient address the original message was incorrect.  Subsequent messages have been delivered.  What an annoyance to have the delivery failure notice reference greylisting when the problem is an invalid address.
[/quote]

Haha - at least it was easily sorted out :)

 I have encountered a delivery problem due to Greylisting so am presenting the following for some feedback and suggestions on workarounds (Mercury v4.8, MercuryE, no SSL):

 The delivery failured notice contains multiple entries of:

   450 4.2.0 <username@acousti.com>: Recipient address rejected: Greylisted, see http://postgrey.schweikert.ch/help/acousti.com.html

   450 4.1.1 <username@acousti.com>: Recipient address rejected: unverified address: Address verification in progress

Following the link I get to this help information which I am hoping for an explanation of.  From: http://projects.puremagic.com/greylisting/

I run a mailserver, and some users say we are being blocked. How do I get off your list?

We do not run a blacklist. There is no centralized list to request checking of your server, or to request removal from.

The reason your mailserver is getting blocked is most likely that it does not properly handle 45x SMTP error codes, and does

not retry delivery within a reasonable amount of time after receiving such a code. Please read the whitepaper

for further technical information. Please, don't contact us asking for removal. Since there is nothing to remove you

from, any requests for removal will be ignored.

 Thanks.

A quick search reveals that some mail servers require the username to be in lowercase (which the rfc's also state). Are the addresses in lowercase?

Have since discovered that the recipient address the original message was incorrect.  Subsequent messages have been delivered.  What an annoyance to have the delivery failure notice reference greylisting when the problem is an invalid address.