Email Deliverability Guide Part 3: Managing Lists, Handling Bounces And Spam

This Email Deliverability Best Practices Guide was originally published by the team at Mailgun. Mailgun is an easy-to-use, API-based email deliverability tool for developers which Rackspace acquired in August 2012. 

In Part 1, we gave an overview of how to maintain a good reputation with email service providers (ESPs) and how to host your email infrastructure if you want to manage email deliverability yourself. Part 2 discussed how IP addresses, sending volume, DNS and authentication affect deliverability. Today, we’ll look at important topics like how to maintain email lists, how to handle bounces and spam complaints.

Managing Mailing Lists

The No. 1 reason we see people get blocked by ESPs is because they have a bad mailing list. Don’t purchase your list or scrape websites for emails. It’s the easy way out and you will pay the consequences. Most of these lists have bad email addresses and include spam traps. ESPs are very good at recognizing bad mailing lists.

You should only send emails to people who have opted in to receiving your emails on YOUR website. In addition, you should send a verification email with a link that confirms their subscription (double opt-in) to make sure their email address is correct and that they are indeed the person that signed up. If everyone did this, the world would be a better place.

You should have your Privacy Policy easily accessible on your website. In addition, you should have a place on your website where users can unsubscribe from your mailings, in addition to a link in every email you send (we’ll cover unsubscribe handling in a future post).

If you’re a Mailgun customer, we give you information for bounces, unsubscribes, complaints, opens and clicks so you can modify your mailing lists appropriately. In addition, we automate a lot of the work by keeping track of recipients that have unsubscribed, bounced or complained and stopping future deliveries to those recipients. We give you various levels of unsubscribe granularity so your recipients can unsubscribe to all emails from the domain, just that mailing list or just emails with a specific “tag” (which you define).

Bounce and ESP Feedback Handling

A big part of maintaining your email reputation is processing bounces properly. While most major ESPs give bounce replies “on the wire” during the SMTP session, there are some that send bounce messages via email. In order receive these emailed bounce messages, you must have the appropriate return path header included with your email so recipients know where to reply with bounce information.

You must also process this bounce data and act accordingly. In addition, many ESPs will soft bounce your initial attempts at delivery. This is also called grey-listing or throttling. If you continue to send emails to bad addresses or you do not listen to ESPs feedback, you will get filtered and eventually your emails will be dropped.

For Mailgun customers, we automatically processes bounce information and react accordingly. A good portion of Mailgun’s technology is devoted to the parsing of this feedback and adjusting your sending in accordance with this feedback so you maintain a good reputation.

If we receive a hard bounce, we will stop sending to that address immediately and will not attempt future deliveries to that address. We will stop sending to an address after multiple soft bounces, according to the ESPs’ guidelines. It is possible to remove addresses from the flagged list in your control panel or through the API, in case it was a temporary issue.

If you are not a Mailgun customer, you should make sure that your provider takes similar actions, or that you have sent up these bounce handling procedures to ensure that you maintain a good sending reputation.

Feedback Loops and Spam Complaints

Most of the major ESPs (other than Gmail) provide feedback loops through which they give you information about spam complaints. Here is a thorough list from Word to the Wise. It is important that you sign up for these feedback loops and pay attention to the feedback you are getting. If you ignore this feedback, ESPs will throttle you and eventually block you completely.

Mailgun registers all of our IPs for these feedback loops. Customers can access this information through the Control Panel, the API or Webhooks. In addition, we process spam complaints automatically and will stop sending to email addresses after a recipient complains. It is possible to remove addresses from the flagged list in your Control Panel or through the API.

That’s it for this time!  In part 4, we’ll discuss unsubscribe handling, recipient engagement and whitelisting.


  1. I’ll post this here, because the e-mail I sent Rackspace about the issue was deleted without being read., who is being hosted by Rackspace, is spamming me. 3 of their “brokers” repeatedly send me emails trying to get me to send money. There is no unsubscribe link in their mails. I have repeatedly told them to stop contacting me. They are even calling me now, after I told them not to ever contact me again. I want something done about them.

  2. Hi Troy,

    We’ll be happy to investigate this for you. Please forward a copy of the email to That email will generate a ticket and the team will dig into the details and take appropriate actions.

    Thanks for letting us know about this!

    Matt Wilbanks


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