Support existing plugins that set PHPMailer to use SMTP

[DJPaul]

Certain plugins configure WordPress to use SMTP for PHPMailer, and don't re-implement wp_mail nor filter enable HTML. An example plugin that does this is "Easy WP SMTP".

Since we use PHPMailer, we ought to try to support these plugins since they're just tweaking how PHPMailer works, rather than re-implementing WordPress' entire email "API".

[djpaul]

In 10635:

Emails: add WordPress' phpmailer_init action to support WordPress plugins that adjust PHPMailer's configuration.

Certain existing popular plugins configure WordPress to use SMTP for PHPMailer, and don't re-implement wp_mail() nor filter to enable HTML. Since we use PHPMailer, we ought to support these plugins since they're just tweaking how PHPMailer works rather than re-inventing the wheel.

We achieve this by adding the phpmailer_init action in addition to our own bp_phpmailer_init action.

Fixes #6945

[djpaul]

In 10636:

Emails: add WordPress' phpmailer_init action to support WordPress plugins that adjust PHPMailer's configuration.

Certain existing popular plugins configure WordPress to use SMTP for PHPMailer, and don't re-implement wp_mail() nor filter to enable HTML. Since we use PHPMailer, we ought to support these plugins since they're just tweaking how PHPMailer works rather than re-inventing the wheel.

We achieve this by adding the phpmailer_init action in addition to our own bp_phpmailer_init action.

Fixes #6945 (2.5 branch)