Intercept outgoing mails in Ruby on Rails

There already are a bunch of solutions for this; including the post_office gem by my co-worker, but this is the simple Unix-y approach for us simple Unix-y folks.

We take advantage of delivery_method = :sendmail, this pipes an email to something executable; this is assumed to be sendmail, but it can be anything.

Append to mbox file

This is similar to setting delivery_method = :file, except that you can read the mails with $any mail client, so you can check formatting, attachments, etc.

config/environments/development.rb:

YourApp::Application.configure do
    # [...]
    config.action_mailer.delivery_method = :sendmail
    config.action_mailer.sendmail_settings = {
        location: "#{Rails.root}/script/fake-sendmail",
        arguments: "'#{Rails.root}/tmp/mail.mbox'",
    }
end

script/fake-sendmail (don’t forget to make this executable):

#!/bin/sh
echo "From FAKE-SENDMAIL $(date)" >> "$1"
cat /dev/stdin >> "$1"
echo >> "$1"

You can read the mbox file from the commandline with mail -f tmp/mail.mbox or mutt -f tmp/mail.mbox.

Most email clients should be able to read mbox files one way or other; although it requires some hackery for Thunderbird:

1. Exit Thunderbird
2. cd ~/.thunderbird/$profile_name/Mail/Local Folders/
3. ln -s ~/code/yourproject/tmp/mail.mbox your-folder-name
4. Restart Thunderbird; you should now have the mbox file in ‘Local Folders’

See also this page.

Forward to another email address

This will only forward all mails to another email address.

config/environments/development.rb:

YourApp::Application.configure do
    # [...]
    config.action_mailer.delivery_method = :sendmail
    config.action_mailer.sendmail_settings = {
        location: "#{Rails.root}/script/fake-sendmail",
        arguments: 'martin+rails@arp242.net',
    }
end

script/fake-sendmail (don’t forget to make this executable):

#!/bin/sh
sendmail -if fake_sendmail@example.com "$1" < /dev/stdin