chore: Make SMTP environment variables configurable (#1868)

fixes: #1647

config/initializers/mailer.rb

@@ -0,0 +1,45 @@
+Rails.application.configure do
+  #########################################
+  # Configuration Related to Action Mailer
+  #########################################
+
+  config.action_mailer.delivery_method = :smtp
+  # We need the application frontend url to be used in our emails
+  config.action_mailer.default_url_options = { host: ENV['FRONTEND_URL'] } if ENV['FRONTEND_URL'].present?
+  # We load certain mailer templates from our database. This ensures changes to it is reflected immediately
+  config.action_mailer.perform_caching = false
+  config.action_mailer.perform_deliveries = true
+  config.action_mailer.raise_delivery_errors = true
+
+  # Config related to smtp
+  smtp_settings = {
+    domain: ENV.fetch('SMTP_DOMAIN', ''),
+    address: ENV.fetch('SMTP_ADDRESS', 'localhost'),
+    port: ENV.fetch('SMTP_PORT', 587)
+  }
+
+  smtp_settings[:authentication] = ENV.fetch('SMTP_AUTHENTICATION', 'login').to_sym if ENV.fetch('SMTP_AUTHENTICATION', '').present?
+  smtp_settings[:user_name] = ENV.fetch('SMTP_USERNAME', '')
+  smtp_settings[:password] = ENV.fetch('SMTP_PASSWORD', '')
+  smtp_settings[:enable_starttls_auto] = ActiveModel::Type::Boolean.new.cast(ENV.fetch('SMTP_ENABLE_STARTTLS_AUTO', true))
+  smtp_settings[:openssl_verify_mode] = ENV.fetch('SMTP_OPENSSL_VERIFY_MODE', 'peer')
+  smtp_settings[:ssl] = ActiveModel::Type::Boolean.new.cast(ENV.fetch('SMTP_SSL', true)) if ENV['SMTP_SSL']
+  smtp_settings[:tls] = ActiveModel::Type::Boolean.new.cast(ENV.fetch('SMTP_TLS', true)) if ENV['SMTP_TLS']
+
+  config.action_mailer.delivery_method = :smtp
+  config.action_mailer.smtp_settings = smtp_settings
+  # You can use letter opener for your local development by setting the environment variable
+  config.action_mailer.delivery_method = :letter_opener if Rails.env.development? && ENV['LETTER_OPENER']
+
+  #########################################
+  # Configuration Related to Action MailBox
+  #########################################
+
+  # Set this to appropriate ingress service for which the options are :
+  # :relay for Exim, Postfix, Qmail
+  # :mailgun for Mailgun
+  # :mandrill for Mandrill
+  # :postmark for Postmark
+  # :sendgrid for Sendgrid
+  config.action_mailbox.ingress = ENV.fetch('RAILS_INBOUND_EMAIL_SERVICE', 'relay').to_sym
+end