Mailers are a feature used in literally every Rails application. But they are often an after thought where we throw out the rules of well-written applications.

Writing mailers is a “set it and forget it” part of your codebase. But recently, I’ve revisited the handful of mailers in my application and I was shocked at both how bad things were and also how many nice mailer features in Rails I wasn’t aware of.

https://boringrails.com/articles/writing-better-action-mailers/