Passing by reference deprecated in PHP 5.3
We now integrated SwiftMailer API in the v4 core trunk (yea!). To do this, I backported the functions which you have created here (the send() helper in the message class).
This uncovered a little bug in getFailedRecipients().
See attached patch which solves it in v4.
[+BUGFIX] SwiftMailer: Fix pass-by-ref and wrong getter
A case of pass-by-reference was fixed and the getter for failed
recipients now actually returns the failed recipients. send() resets
the failed recipients now.