General :: Windows - Why Does E-mail Render Incorrectly Only For Certain Recipients - When Use A Certain Server

This has been driving me absolutely crazy for a few days now. I have an e-mail. If I send it from a Windows Server 2003 server via MailEnable, a certain person receives it using Outlook 2003 just fine. If, however, I send the exact same message from an Ubuntu 10 server using SSMTP to relay the e-mail to the exact same MailEnable queue, the recipient receives a messed-up-looking e-mail. There are all kinds of "= " all over the place. The exact same e-mail looks fine on my Ubuntu computer, as well as my Mac, and all of the Windows/Mac computers here at work. Here is an excerpt from the copy they receive:

COMPANY has been communicating with COMPANY as they Agency worked to develop the= COMPANY permit, knowing that this would impact aquatic pesticide applicat= ion. But in December, COMPANY advised us that the COMPANY permit would = also cover any pesticide applications made "on or near any water or water c= onveyance." They described a scenario in which a pesticide applicatio= n made in a field or pasture that had a waterway or ditch in it (even if th= e waterway or ditch was dry) would need a COMPANY permit. This meant th= at the majority of pesticide applications made to crops would need a COMPANY = permit, and would have to comply with all the burdensome paperwork requirem= ents plus all of the pesticide application records would be available to th= e public for review.

What on Earth is happening? I'm using PHP's Mail_Mime to send the mail, if that matters.

I have tried testing this on an in-house netbook, running XP and Outlook 2003, same as them, and it looks fine. Unfortunately though, it's happening for more than one person, with different companies, in different states. Is it maybe an Outlook thing? Or a firewall?

Here are the headers they sent me, when I requested them earlier: