Our app is currently experiencing very high signup volume and our users are getting errors when trying to sign up due to the email confirmation rate limits by Supabase (100/hr for pro plans). We're trying to switch to custom SMTP for this, I've made a Mailgun account and added my SMTP information to the auth settings and it isn't working. When trying to sign up on our app, we get this error message: 'code":500,"msg":"Error sending confirmation mail' Any ideas of what we could be doing wrong? All of the SMTP information entered is correct so I'm not sure why it wouldn't be processing the emails properly. This is severely limiting our users since only 100 per hour can sign up.

Unless there is a brand new issue, custom SMTP works (and no one is reporting an issue). So likely in your setup or your mailgun account setup. You would need to provide more info for any user here to help you (if they can or have ideas). https://github.com/orgs/supabase/discussions/7444 I see several issues/solutions googling

mailgun supabase smtp

If you are paid plan you can also ask for support assistance.