Has anyone seen this issue sending mail out SMTP server?

Good Morning,

I have a user who sent an email to approx 40 people outside of our college. They all came back undeliverable. When looking at the mail routing logs, I see the message ID leave the users mail server and go to out SMTP server.

On the SMTP servers mail routing logs I see this for all the messages when they leave the SMTP server to go to our Spam Filtering device:

02/11/2010 05:39:20 PM Router: Message 0081ED89 transferred to 10.1.1.111 for =?UTF-8?B?4oCqbGluZGEuZXNrZXJAY3J5c3RhbGZpbmlzaGluZy5jb23igKw=?= 0xLK202AzJonSmith@XYZCorp.com0xLK202Cz via SMTP

Somehow extra characters are added to the front and end of the email address.

Just hoping someone can explain what possibly happened here.

thank you in advance.