The following error may occur if the Mandrill WordPress plugin is installed and activated while there exist another plugin on your WP setup which tinkers with the email settings on your WordPress:
wp_mail has been declared by another process or plugin, so you won’t be able to use Mandrill until the problem is solved.
How to Fix This wpMandrill Plugin Conflict
- Deactivated ALL plugins except WP Mandrill.
- If the error message disappeared then it’s not a theme conflict.
- Activated each plugin one by one, until the error message appears again (in my case Heartbeat Control).
- Deactivate or remove the plugin.
- Next activate all other necessary plugins.
- Finally, add Mandrill settings and test to see everything worked.
What if you NEED the plugin which conflicts?
If you need the plugin which conflicts with wpMandrill, you have 2 options: don’t use wpMandrill; or fix the plugin in question (email the plugin developer and be very nice… you never know, they might want to help you get this fixed! )