A suppression list is a list of contacts that you do not want to send to because sending to these contacts could hurt your sending reputation and delivery rates. 

The suppression list is required by the CAN-SPAM Act to ensure that email senders have a method of opting-out recipients who unsubscribed or marked email as spam. The suppression list also collects emails that bounce, are blocked, or invalid. 

We’ll walk through why the suppression list is so important for your sending reputation, as well as a few email marketing use cases. 

What does a suppression list include?


When a recipient unsubscribes from your emails, their address should be immediately added to a suppression list. The suppression list informs your email program to stop sending to that contact. 

So are unsubscribe groups and suppression lists one and the same? Not quite. Think of the 2 as yin and yang—you can’t have one without the other. The unsubscribe group is what the recipient clicks to inform the sender they’d no longer like to receive emails, while the suppression list is what the sender uses to suppress sending to unsubscribed recipients.

If you didn’t have a suppression list, clicking the unsubscribe link wouldn’t do anything (yikes!). You would end up sending to recipients who previously unsubscribed, making those recipients much more likely to mark your email as spam. 

Luckily in Twilio SendGrid’s platform, you are required to enter an unsubscribe group, which automatically creates a suppression list. You don’t have to worry whether or not your unsubscribed recipients are being sent email.

Pro tip: Make it easy for recipients to find your unsubscribe link. If they can’t find it, the alternative is to flag your email as spam (and no one wants that!). 

Spam complaints

The suppression list also collects addresses that mark your message as spam. Sending to recipients after they submit a spam complaint is terrible for your sending reputation. It informs ISPs that you send unwanted emails and do not listen to your recipients. This could lead to the deny listing of your IP address or domain.

Pro tip: To avoid getting sent to the spam folder in the first place, follow best practices in our article, Why Are My Emails Going to Spam?

Bounced, blocked, or invalid addresses

In addition to unsubscribes, the suppression list contains email addresses that bounce, are blocked, or invalid. If you continue sending to these addresses it would affect your delivery rates, telling ISPs that you do not make the effort to keep your contact list clean, and therefore, aren’t a trustworthy sender.

Pro tip: Send to valid email addresses with our Email Validation API. It uses machine learning to detect invalid, misspelled, or nonexistent addresses which will improve your sender reputation and delivery rates.

Suppression lists in email marketing

While suppression lists are useful to help you send to the right contacts, they also allow you to control the frequency and content sent to specific users. 

In Twilio SendGrid’s platform, you can set up a preference center that contains multiple unsubscribe groups. Each unsubscribe group is connected to its own suppression list. This allows users to unsubscribe from certain types of email without unsubscribing from all of your email.

Providing valuable and relevant content keeps your recipients happy and engaged, making suppression lists a useful tool to email marketers. Check out a few ways you can use suppression lists below to create a better experience for your recipients.


The frequency of your email campaigns, especially during the holidays, can overwhelm your recipients. To give your recipients a better experience during the holidays, ask if they’d like to opt-out of holiday email or choose to reduce their sending frequency leading up to the holidays.

In this scenario, the recipient would not fully unsubscribe.  They would be added to a specific suppression list for the months of November and December letting your email program know not to send to them for the next couple of months. Then in January, you would pick back up sending to the recipient.


Let’s say your recipient enjoys your weekly newsletter, but would like to stop receiving your daily deals email. If you provide options in your preference center, your recipient can unsubscribe from the daily deals and still receive the weekly newsletter.


If you have product-related emails, a recipient could choose to receive product emails specific to the product they like or own. All other emails they could opt-out of via a preference center where they would then be added to a suppression list specific to the product-type.

Pro tip: Update your preference center to include frequency options and/or the variety of emails you send. Check out these examples


Suppression lists allow you to automatically stop sending to recipients who no longer want your email. They also give your recipients the option to adjust frequency and content according to their interests. This helps keep your recipients happy and your sending reputation strong. 

To see how you can manage suppression list and unsubscribe groups at Twilio SendGrid, take a look at our docs page

Julie is the content marketing manager at Twilio SendGrid, helping to write and edit the blog, as well as enhance SendGrid’s SEO efforts. When she isn’t at the office, you’ll find her buzzing around Denver’s coffee shops, breweries, and yoga studios.