I would like to alter the Message-ID
header that is in the header portion of an email sent from a Ruby on Rails v3 application using ActionMailer.
I am using Sendmail on localhost for mail delivery.
Do I configure this in Sendmail or ActionMailer?
Where do I configure this (if it is ActionMailer): a file in config/
folder or a file in app/mailers/ folder?
Teddy's answer is good, except that if you actually want each message to have a different ID, you need to make the default a lambda. In the first block of code in his answer, it calculates the message-ID once, at init, and uses the same one for every message.
Here's how I'm doing this in my app:
default "Message-ID" => lambda {"<#{SecureRandom.uuid}@#{Rails.application.config.mailgun_domain}>"}
... with the domain taken from a custom app config variable (and using SecureRandom.uuid, which is a little more straightforward than a SHA-2 based on the timestamp IMO.)