Disable implicit mulitplexing in PHPMailerLite
Summary:
PHPMailerLite implicitly multiplexes mail, but we multiplex mail in an application-aware way higher in the stack. Disable the multiplexing.
The actual option is here: https://secure.phabricator.com/diffusion/P/browse/master/externals/phpmailer/class.phpmailer-lite.php;03dafec74f97bcd7$166
Test Plan: @klimek confirms this fixes his issue.
Reviewers: klimek, vrana, btrahan
Reviewed By: vrana
CC: aran
Differential Revision: https://secure.phabricator.com/D3365