Any update on this?
Threaded topics quickly become unusable, and I’ve been unable to find any way to improve performance.
I ended up getting this working by ditching wpMandrill plugin and using Easy WP SMPT plugin https://wordpress.org/plugins/easy-wp-smtp/
After some more digging, I see that Mandrill is rejecting emails sent to noreply@<domain>
So perhaps this rejection is causing WordPress to send the email instead?
