[imp] IMP causing an HTTP Error 406 when sending mail

[Brian Voils]

For some reason, IMP is causing an HTTP Error 406 whenever I try to
send mail to an AOL e-mail account.  It doesn't have any problems with
sending to other domains, but for every account I use, it errors out
when trying to send to an AOL account (@aol.com).  I haven't made any
changes to the system, it's just started.  I imagine it's a corrupt
file or something.  The error is certainly in my installation of IMP,
though, because my hosting company has their own installation (which
is very cumbersome to login to) and does not have the same problem.
Any ideas what's going on?

It's installed on a shared server, and I don't have shell access.
They do have a terrific helpdesk, however, and can do just about
anything on the shell for you, if needed.  I have FTP access and do
have filesystem access, however.

Anyways ...

Version Information:
IMP Version 3.2.3
Horde Version 2.2.5
PHP Version 4.3.11
Apache/1.3.33 (Unix) mod_auth_passthrough/1.8 mod_log_bytes/1.2
mod_bwlimited/1.4 PHP/4.3.11 FrontPage/5.0.2.2635 mod_ssl/2.8.22
OpenSSL/0.9.7a
Linux server54 2.4.21-32.0.1.ELsmp #1 SMP Wed May 25 14:26:33 EDT 2005 i686