Weird Email Issue

basically we running commbulletin and add on for Vbulletin which sends out newsletters to all the members of the forum

We sent out a newsletter last month

It has the usual details to fill in

name:
From address
Subject:
header:

ok we did all that and for name we just put down

"My name"

for the from address field we put down
"Our Organisation" (Just the words not any email address or anything - just as how i've spelt it)

Now the problem is that once of our users who uses outlook to retrieve their emails when they got the email in the FROM header it appeared something like this

"Our Organisation"@thecompanydomains name

now of course they know think somehow we forged the email to make it look as if that it was being sent from their domain which it wasnt since all the headers originates from our server

however my point is how is that possible that when this email was sent the FROM field had that on

does that make sense