I am implementing background email processing with Resque using the resque_mailer gem (https://github.com/zapnap/resque_mailer). I was able to get it to work for all my emails except the ones sent by Devise.
I went through a bunch of SO questions, and blog posts (for instance http://teeparham.posterous.com/send-devise-emails-with-resque) but could not find a way to get it to work.
What are the precise steps to follow to get resque_mailer to work with Devise?
I'd take a look at devise-async. Looks like it fits your use case. Devise Async