December 2022 Summaries

Mailtrap’s ActionMailer Balancer is a Ruby on Rails ActionMailer extension that distributes outgoing email traffic between two delivery services according to configurable percentages, such as sending most messages through an existing provider while gradually increasing traffic through a new one. It is intended to support gradual ESP migrations, transitions from SMTP to API configurations, load sharing, and backup delivery arrangements while helping preserve deliverability, sender reputation, and IP warm-up progress. The gem works with built-in or third-party ActionMailer delivery methods, selects a service before ActionMailer sends the message, operates within the application without additional plugins, and supports shared or dedicated IPs. Setup involves installing the gem, configuring delivery methods, credentials, and traffic weights, then continuing to use ActionMailer normally; users also need appropriate SPF DNS records for each connected provider.