According to the PHP Manual for mail(), the lines in the message must be 70 chars long max. and should be separated with \n (LF). While I've never encountered a problem caused by this, you can give it a try.
Oh, I generally write down message HTML in a single string like:
$message = '
<div>
<span>...
...etc...
';
So it's getting newlines automatically. You can simply trim $strBody=$strBody."
parts and concatenate the message into a single multiline string.
If you can't get it working, you can try ready-made classes like Zend Mail.