If you have your ActiveJob and concurrency library set-up is done documentation here.The most simple solution is to override you device send_devise_notification instance methods involved with the transactions mails like shown here
class User < ApplicationRecord
# whatever association you have here
devise :database_authenticatable, :confirmable
after_commit :send_pending_devise_notifications
# whatever methods you have here
protected
def send_devise_notification(notification, *args)
if new_record? || changed?
pending_devise_notifications << [notification, args]
else
render_and_send_devise_message(notification, *args)
end
end
private
def send_pending_devise_notifications
pending_devise_notifications.each do |notification, args|
render_and_send_devise_message(notification, *args)
end
pending_devise_notifications.clear
end
def pending_devise_notifications
@pending_devise_notifications ||= []
end
def render_and_send_devise_message(notification, *args)
message = devise_mailer.send(notification, self, *args)
# Deliver later with Active Job's `deliver_later`
if message.respond_to?(:deliver_later)
message.deliver_later
# Remove once we move to Rails 4.2+ only, as `deliver` is deprecated.
elsif message.respond_to?(:deliver_now)
message.deliver_now
else
message.deliver
end
end
end