3 Action Mailer Features I Didn't Know Existed

A few weeks ago I needed to check something in the Action Mailer docs, just a quick lookup. I ended up spending much more time there than expected and found a few features I had no idea existed, even though I've been using Action Mailer in production for a while. One of them lets you see an email before it's ever sent. Another lets you modify an email right before it goes out. And the third one allows you to override the default delivery options dynamically. I figured I probably wasn't the only one who had missed these, so here are three Action Mailer features that caught my attention. If you want to explore more, the official Action Mailer documentation is always a great place to start. 1. Previews Before I found this, testing an email meant sending it to myself, checking my inbox, tweaking the template, and repeating. Turns out ActionMailer has a built-in way to preview emails in the browser, without sending anything. You add a preview class in test/mailers/previews like: class InvitationMailerPreview < ActionMailer :: Preview def team_invitation InvitationMailer . with ( user: User . first , company: Company . first ). team_invitation end end And visit http://localhost:3000/rails/mailers/invitation_mailer/team_invitation . This removes the usual feedback loop of tweaking a template. You just refresh the browser instead. Rails also allows custom preview paths if you want to keep previews in a different location: config . action_mailer . preview_paths << " #{ Rails . root } /lib/mailer_previews" This was a small discovery, but it immediately improved my workflow. 2. Interceptors An interceptor is a hook that runs right before an email is handed off for delivery, letting you modify it. A common use case is preventing mistakes in staging environments. Nobody wants to accidentally send a real looking email from a staging application to an actual customer. Another common approach is redirecting all outgoing mail in staging or development environments to a single defaul