Rails 7.1 Multiple SMTP Provider

application_mailer.rb

class ApplicationMailer < ActionMailer::Base
  default from: '"ZZZ" <[email protected]>'

  private

  def gmail_delivery
    mail.delivery_method.settings = Rails.application.secrets.gmail_smtp
  end

  def mandrill_delivery
    mail.delivery_method.settings = Rails.application.secrets.mandrill_smtp
  end

  def mailgun_delivery
    mail.delivery_method.settings = Rails.application.secrets.mailgun_smtp
  end
end

config_secrets.yml

production:
  gmail_smtp:
    :authentication: "plain"
    :address: "smtp.gmail.com"
    :port: 587
    :domain: "zzz.com"
    :user_name: "[email protected]"
    :password: "zzz"
    :enable_starttls_auto: true
  mandrill_smtp:
    :authentication: "plain"
    :address: "smtp.mandrillapp.com"
    :port: 587
    :domain: "zzz.com"
    :user_name: "[email protected]"
    :password: "zzz"
    :enable_starttls_auto: true
  mailgun_smtp:
    :authentication: "plain"
    :address: "smtp.mailgun.org"
    :port: 587
    :domain: "zzz.com"
    :user_name: "[email protected]"
    :password: "zzz"
    :enable_starttls_auto: true

my_mailer.rb

class MyMailer < ApplicationMailer
  before_deliver :gmail_delivery, only: :newsletter
  before_deliver :mailgun_delivery, only: :reset_password_instruction

  def newsletter
    # ...
  end
  
  def reset_password_instruction
    # ...
  end
end