How to set sidekiq options for ActionMailer / ActiveJob / MailDeliveryJob

code.rb

# in default config, ActionMailer will use sidekiq wrapped in ActiveJob
# This makes it so there is no obvious/direct place to specify configuration
# It's easy to do with the below method, which can be placed in an initializer

Rails.application.config.after_initialize do
  ActionMailer::MailDeliveryJob.class_eval do
    sidekiq_options retry: 2
  end
end

# n.b. This does NOT work, because initializers run before the railtie which sets
#      up the ActionMailer / ActiveJob / sidekiq relationship
# ActionMailer::MailDeliveryJob.class_eval do
#   sidekiq_options retry: 2
# end
# but it can be used for other non-sidekiq things,
# e.g. https://github.com/mastodon/mastodon/blob/main/config/initializers/mail_delivery_job.rb