Why does str_replace of \n introduce '!' in mail content?

Question

$mailContent=str_replace(" "," ",$mailContent); $mailContent=str_replace("\n"," ",$mailContent);

Why do the above lines introduce '!' at random points in my mail content?

Input:

http://pastebin.com/7eG6d3SH

Output:

Answer 1

I actually had a huge problem with this just yesterday.

Basically, your lines are too long, and out of desperation it's throwing in !\n to break it up so it can be transmitted effectively.