The $phpmailer class is currently used to enable sending of emails through the wp_mail function defined in wp-includes/pluggable.php
The wp_mail function handles some header information before passing the rest through the AddCustomHeader? function.
My plugin (subscribe2) uses the BCC header to send an email notification to a list of users when a new post is made. RFC 2822 (http://www.ietf.org/rfc/rfc2822.txt) lists some restriction over the character length of any header and I'm not sure if AddCustomHeader? deals with this limitation.
By adding some code to pluggable.php we can make better use of the AddCc? and AddBcc? functions to create better email headers.
