sijumon

I am using Thunderbird as mail client and working fine.but recently I am sticking on a problem that last week I had send a mail to my three friends.A couple of my friends got the mail successfully but unfortunately the third one got the mail in a corrupted format like in the sense the words and sentences spread out over the sheet in an incorrect format. So that I had tried to send the mail again and again but unfortunately he is getting the mail in the same corrupted format. But the other two friends forwarded that mail to the third one, then he got the mail in the original format.I wonder how this happens?.Can anybody suggest a solution?: