[@robin-w Moderator 8 years, 9 months ago]

It wasn’t until I started googling this that I notice it is a recurring issue with bbpress sites using smtp, and hasn’t got a definitive answer.

As far as I can see two things seem to help.

1. amending the from address
2. not sending bulk emails

this plugin seems to address these two issues

Can you try it and report back

AsynCRONous bbPress Subscriptions

also there is a code snippet that lets you change the from address that smtp may well need -I don’t think it is needed as the plugin does this I hope (I haven’t tested the plugin), but quoted just in case 🙂

However, something causes that in the forum post notifications the “From” is set back to the default <noreply@domain.com>, although it is set to different/custom address by the WP Mail SMTP plugin. My web hosting service blocks the PHP mails sent from unknown addresses, so that’s the reason why the e-mails are not delivered.

/*BBPress email fix*/
add_filter( 'wp_mail_from_name', 'email_sent_from_name' );
function email_sent_from_name( $name )
{
    return 'SITE NAME';
}
add_filter( 'wp_mail_from', 'email_sent_from' );
function email_sent_from( $email )
{
    return 'email@example.com';
}