Broken with WP 4.4.1 which ships with PHPMailer 5.2.9

https://core.trac.www.ads-software.com/browser/tags/4.4.1/src/wp-includes/class-phpmailer.php#L20

It’s PHPMailer 5.2.14, so has getCustomHeaders().

Oh, sorry, I hadn’t thought of checking the sources on WP’s Trac.

Would it be possible that Debian ships a WordPress in version 4.4.1 with PHPMailer 5.2.9 for some reason or another?

I just checked again an I definitely have version 5.2.9 in a WordPress installation that has 4.4.1 written all over it:

class PHPMailer
{
    /**
     * The PHPMailer Version number.
     * @type string
     */
    public $Version = '5.2.9';

I just upgraded to 4.4.2 and it still ships with phpmailer 5.2.9. But I guess this is a fight I will need to take up with Debian Maintainers in this case then. Thanks for your quick response!

Simply to follow up for anyone else stumbling on this issue too:
WordPress in Debian uses the libphp-phpmailer package, which is indeed still version 5.2.9 on Jessie, although WP is available in 4.4.2.

libphp-phpmailer:
  Installed: 5.2.9+dfsg-2+deb8u1
  Candidate: 5.2.9+dfsg-2+deb8u1
  Version table:
 *** 5.2.9+dfsg-2+deb8u1 0
        500 https://debian.mirror.root.lu/debian/ jessie/main i386 Packages
        500 https://security.debian.org/ jessie/updates/main i386 Packages
        100 /var/lib/dpkg/status

I will file a bug report with Debian later today.

Anyone interested in following this up, here’s a link to the jessie-backports mailing list where this bug report ended up: https://www.eenyhelp.com/answer/bug-818758-wordpress-plugins-depending-libphp-phpmailer-5-2-10-help-215986354.html