Handling Bounced Email with Ruby and TMail

If you are using a Ruby on Rails app, or Nitro, or just a plain Ruby application that handles email, you will need to handle at some point, bounced messages. This a simple way to get to the guts of the email and find out what the error codes are…

Here we go:

We need to get an email to handle, so something like:

mail = TMail::Mail.parse(message)

Then, we need to check if this is a bounced email or not, so:

mail.content_type == 'multipart/report'

This will return true or false, if it is true, we need to do more handling to find out the error codes etc.

So, first, find the part of the email that has the message/delivery-status section like this:

delivery_status_part = mail.parts.detect do |part|
  part.content_type == 'message/delivery-status'
end

Now we have the delivery status part, we need to pull out the keys and values, a delivery status body will usually look something like this:

Reporting-MTA: dns; mail9.mail.com.au
Received-From-MTA: DNS; 60-1-1-1.static.mail.com.au
Arrival-Date: Wed, 2 Jan 2008 20:38:15 +1100

Final-Recipient: RFC822; your_address@address.com
Action: failed
Status: 5.0.0
Remote-MTA: DNS; mx1.mail.yahoo.com
Diagnostic-Code: SMTP; 554 delivery error: dd This user doesn't have a
 address.com account (your_address@address.com) [0] -
 mta813.mail.yahoo.com
Last-Attempt-Date: Wed, 2 Jan 2008 20:38:18 +1100

Notice the nice and handy key value pairs separated by ‘:’ ? This makes pulling the main data we need easy by doing:

lines = delivery_status_part.body.split("\n")
info = lines.inject({}) do |hash, line|
  key, value = line.split(/:/) 
  key.downcase! rescue nil
  hash[key] = value.strip rescue nil 
  hash 
end

Now we have a hash that looks like:

{"status"=>"5.0.0",
 "diagnostic-code"=>"SMTP; 554 delivery error",
 "remote-mta"=>"DNS; mx1.bt.mail.yahoo.com",
 "arrival-date"=>"Wed, 2 Jan 2008 20",
 "action"=>"failed",
 nil=>nil,
 "reporting-mta"=>"dns; mail9.tpgi.com.au",
 "final-recipient"=>"RFC822; Angelina@btinternet.com",
 "received-from-mta"=>"DNS; 60-241-138-146.static.tpgi.com.au",
 "last-attempt-date"=>"Wed, 2 Jan 2008 20"}

The nil there in the middle is from the Diagnostic-Code line that wraps. I am not handling unfolding the line in this as to get the details we need, we don’t need to.

So, now we have a key/value hash, we can pull the data we need very easily:

info['status']          #=> "5.0.0"
info['final-recipient'] #=> "RFC822; Angelina@btinternet.com"
info['action']          #=> "failed"
info['diagnostic-code'] #=> "SMTP; 554 delivery error"

Now you can do whatever you want to the message.

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