Rails 7 Ruby 3.1 LoadError: cannot load such file -- net/smtp

Question

I upgraded to Rails 7 and Ruby 3.1. While trying to run tests with rspec I got the error below. How can I fix it?

An error occurred while loading rails_helper.
Failure/Error: require File.expand_path('../config/environment', __dir__)

LoadError:
  cannot load such file -- net/smtp
# .../gems/mail-2.7.1/lib/mail.rb:9:in `<module:Mail>'
# .../gems/mail-2.7.1/lib/mail.rb:3:in `<main>'
# .../bundler/gems/rails-6a0f6c4d70b1/actionmailbox/lib/action_mailbox/mail_ext.rb:3:in `<main>'
# .../bundler/gems/rails-6a0f6c4d70b1/actionmailbox/lib/action_mailbox.rb:3:in `<main>'
# .../bundler/gems/rails-6a0f6c4d70b1/actionmailbox/lib/action_mailbox/engine.rb:9:in `<main>'
# ./config/application.rb:11:in `<top (required)>'
# ./config/environment.rb:2:in `require_relative'
# ./config/environment.rb:2:in `<top (required)>'
# ./spec/rails_helper.rb:4:in `require'
# ./spec/rails_helper.rb:4:in `<top (required)>'

(bootsnap and zeitwerk is excluded from backtrace)

Answer 1

For Rails 6

Add gem 'net-smtp', require: false to your Gemfile and run bundle.

Similarly I assume you may have problems with net-imap and net-pop and so have to add them until a new mail gem version is released.

gem 'net-smtp', require: false
gem 'net-imap', require: false
gem 'net-pop', require: false

UPD: The mail gem version 2.8.0 was released on December 3rd, 2022 which includes the fix. Just upgrade to >= 2.8.0.

For Rails 7

On January 6th, 2022 Rails 7.0.1 was released:

The focus of this release is bring support to Ruby 3.1

Amongh other Ruby 3.1-related issues it brought a fix for this problem. So upgrade to Rails >= 7.0.1.

---

Related pull requests and issues:

• mikel/mail: Add former default gems as a dependency for Ruby 3.1 compatibility
• Add net/smtp gem for bug report templates to support Ruby 3.1

Answer 2

I met the same problem when running Rails in production mode. ( Ruby 3, Rails 6.1 )

copy and paste this lines of code to Gemfile:

gem 'net-smtp', require: false
gem 'net-imap', require: false
gem 'net-pop', require: false