Anyone noticing some "quirkiness" happening when they use the eZ Mail component in their scripts and bounce the messages off of a Qmail server, might want to check out this helpful hint from Tobias Schlitt on how he solved it.
While working with the eZ Mail component, for sending some emails comfortably, I noticed some issue with my Qmail installation. With some email accounts that received the emails, the headers were broken and had double line break characters, so the complete email was broken. That (weirdly) happened only with some servers (e.g. Gmail), while my own server handeled the emails gracefully.
He discovers that the issue lies on Qmail's side, where the sendmail wrapper for it looks for a "n" instead of a "rn" line PHP sends at the end of a line. Thankfully, it's an easy fix with the eZ Mail component:
ezcMailTools::setLineBreak( "\n" );