How to get mailcatcher to work with rbenv, bundler, and ruby 3.2.0?

I've completely removed rvm and installed 0.5.10 of mailcatcher. When I run mailcatcher I get the following error:

.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/activesupport- `<class:BigDecimal>': undefined method `new' for BigDecimal:Class (NoMethodError)'4.56').dup

What could be causing the error?


  • Mailcatcher version 0.5.10 was released in September 2012, more than 10 years ago. And this ancient version requires activesupport ~> 3.0 which is part of Ruby on Rails and therefore adding it to your Gemfile and running Bundler, downgraded your application's Rails version to the latest 3.2 version.

    To fix this problem, I suggest adding Mailcatcher to your Gemfile without specifying any version, like this

    gem 'mailcatcher'

    and running bundle install again.

    That should install the latest version of the Mailcatcher gem (0.8.2 at the time of writing this answer) which should run fine with up-to-date versions of Ruby on Rails.