Redmine

My Redmine installation is authenticating users off LDAP and I'm accepting e-mail Issue submission. Here is the alias I've created on my mailhost:

<user>: "|/root/scripts/rdm-mailhandler.rb --url=http://<FQDN> --key=<key> --project=<PROJECT> --tracker=Support --allow-override=tracker --unknown-user=accept"

This works for every user (thus far) except one in particular, who DOES exist in both LDAP and Redmine, but whenever he specifically sends an e-mail to Redmine, we get an "Unprocessable Entry" message in the logs:

Processing MailHandlerController#index (for <IP_ADDRESS> at 2010-01-26 09:17:24) [POST]
Session ID: b22225f66268e7b54a9bb06dbe5a5358 Parameters: {"unknown_user"=>"accept", "action"=>"index", "allow_override"=>"tracker", "controller"=>"mail_handler", "issue"=>{"project"=>"<PROJECT>", "tracker"=>"Support"}, "key"=>"<KEY>",......
.......
Completed in 0.01551 (64 reqs/sec) | Rendering: 0.00024 (1%) | DB: 0.00724 (46%) | 422 Unprocessable Entity [http://&lt;REDMINE_SERVER&gt;/mail_handler]

At first I had thought that maybe his e-mail syntax was off, but I have submitted the issue as both myself and another user and both time it went through and created the issue in Redmine.

THEN...

So this is actually happening to several users.

At first I thought it may be due to HTML in an email, so we tried a user who couldn't get his mail through, using plain text. Still not working.

Has anyone seen where their Exchange SERVICE (we don't have it in-house) does something to mail? With kmail, it works for one user, from OWA and Entourage, not at all.

FINALLY...

I've also attempted to connect directly to my mail host and send the EXACT same message from users that I were working and ones that were not. The same thing keeps happening to the users that were not working (for submitting through e-mail) - they get a 422 Unprocessable Entity Error.