From memory, there is the same bug with newsletters and with wiki page change notifications.
The bug appears in some mail clients (ex.: IMP webmail and gmail) but not others (Thunderbird). I am using Linux servers.
I have a temporary fix in notificationemaillib.php
< $smarty->assign_by_ref('mail_pagedata', $edit_data);
> $smarty->assign_by_ref('mail_pagedata', str_replace "\r\n", "\n", $edit_data));
I didn't commit because I am prety sure it is not a good way to solve this problem.
There is a "Mail end of line:" setting in tiki-admin.php?page=general which is supposed to help here but it hasn't worked for me.
I have noticed the same problems with text emails sent by phplist, therefore I think it is a bug in the email transfer class:
Maybe we should upgrade to the latest version?