Protect your sending reputation with email suppression lists

Šarūnas Ročevas Šarūnas Ročevas
· 32 min read · Tips and resources · April 28th, 2021
The people on your list that you're not emailing are just as important as the ones you are. Learn how to protect your sending reputation with email suppression lists.

Warren Buffett once said, "It takes 20 years to build a reputation and 5 minutes to ruin it. If you think about that you'll do things differently." While the famed investor may not have been talking about email senders, his words ring true for your sending reputation.

Thankfully, you don’t have to wait 20 years to build your reputation as a sender, but you could easily lose it in an instant. Careless sending practices affect your deliverability and your ability to land in the inbox.

The good news is that you can do things differently. Learn how to use suppression lists to stop sending emails to addresses that damage your sending reputation.

What is a suppression list?

An email suppression list is a contact list of recipients that you do not want to send emails to. These people are in the suppression list because their email addresses are invalid. Contacting them will harm your sender reputation and put your domain at risk of being blocklisted by major ISPs like Gmail.

For example, if you continue to send email messages to a hard-bounced address, not only does your behavior look spammy but inactive emails may be repurposed into spam traps—landing you on a watchlist of errant senders from which it is difficult to leave.

How email suppression lists work

1. Suppressed emails are automatically added

MailerSend takes care of the suppression list for you on the backend. Emails that affect your sending reputation—hard bounces, unsubscribes and spam complaints—are automatically added to the suppressions lists. And you can also manually add emails.

Suppressed emails

2. Suppressed emails are automatically blocked

Next, when you send a transactional email to a recipient via SMTP or email API, MailerSend will check their email address against your suppression lists. If there is a match, the recipient is automatically suppressed and blocked from receiving emails. You’ll be able to see emails that have been blocked on your Activity tab.

Activity tab

Types of email suppression lists

MailerSend makes it easy to manage your email suppression list with an intuitively designed Suppressions manager. First, sign up and verify your MailerSend account if you don’t already have one! Then navigate to Suppressions under your profile photo.

MailerSend dashboard

If you are using multiple domains in MailerSend, the suppression lists are unique to each domain. Thus, you can filter results based on your different domains. This is useful for agencies handling many sending domains for their clients under one account.

Our suppressions help article is always available whenever you need help with suppressions settings in MailerSend.

Your suppression list is conveniently divided into four main categories in MailerSend: hard bounces, spam complaints, unsubscribes, and the blocklist. Clicking on a tab will show you the suppressed emails listed under each category. 

1. Hard bounces

Hard bounced emails are those that cannot be delivered successfully due to permanent email errors such as a non-existent mailbox. These emails are automatically added to the suppression list because they pose the greatest risk to your sending reputation.

The Hard bounces tab does not include soft bounced emails, those emails returned to the sender because of non-permanent errors like a full inbox or a spam filter. These are seen as email errors that will hopefully be resolved without harming your reputation.

Hard bounces tab

2. Spam complaints

A spam complaint occurs when a recipient reports your email as spam. Their email is automatically added to the suppression list under the Spam complaints tab if their ISP supports feedback loops (FBL).

The FBL service—where spam complaints are reported back to MailerSend after your email is marked as spam—is supported by major ISPs like Verizon Media (AOL and Yahoo!), (Hotmail) and QQ (Tencent).

Spam complaints tab

How about the 800-pound gorilla, Gmail? I’m glad you asked! Gmail offers FBL but their service is only available for email service providers (ESPs), such as MailerSend. Thus, Gmail users who report emails as spam will not appear in the spam complaint list here.

3. Unsubscribes

An unsubscribe request happens when a recipient clicks on an unsubscribe link in your email or through the List-Unsubscribe header. If unsubscribe tracking is enabled in MailerSend, their email address is automatically added to the email suppression list.

Here’s an example from a MailerSend template with an unsubscribe link at the bottom of the email.

MailerSend template email

When unsubscribe tracking is enabled, MailerSend gives you peace of mind as unsubscribed email addresses are automatically added to the Unsubscribes tab. You don’t have to worry whether you’ll email someone that has unsubscribed from your list.

Unsubscribes tab

This help article describes all the unsubscribe options that are available to you, including the use of List-Unsubscribe headers and unsubscribe links in your emails.

4. Blocklist

Sometimes you may want to avoid emailing certain recipients. You might have discovered catch-all domains while verifying your email list with a checker like MailerSend's inbuilt email verification tool. Or perhaps you need to block someone that asked you to delete their data for GDPR purposes. Such blocked email addresses are listed here under the Blocklist tab.

Blocklist tab

MailerSend’s blocklist contains emails or custom patterns that you have added manually. Recipients in your blocklist will not know that they have been blocked. For example, if competitors have signed up for accounts, you can stop messaging them by blocking domain names like

Note: Look out for a future feature from MailerSend where you can delete a recipient, for example, for GDPR purposes. Deleted recipients are automatically added to the blocklist and can be retrieved whenever necessary.

Managing your suppression lists

You can manage the email addresses listed under the hard bounces, spam complaints, unsubscribes and blocklist tabs. Either click on the individual checkboxes next to the emails or click the “more” icon to select the range of emails that you want to work with.

Selection options

Then click on the Action button to see a drop-down list of options, including deleting the emails or exporting them in CSV format. Exporting lists is useful if you want to use suppressions data in your workflow, like syncing unsubscribed recipients with your marketing platform using Zapier integration.

Export options

Adding emails to suppression lists

If you’re moving from another ESP or email suppression tool, you can easily import your old suppression list into MailerSend. Choose the list you want to update and then click on Add emails. Then upload a CSV or TXT file, or copy and paste the emails.

Add emails

For blocklists, you can also specify a word pattern. For example, if you enter "5575", emails like eric5575@domain.tld or email@eric5575.tld will be rejected during sending. If you want to block a specific domain, you can add it as @eric5575.tld, for example.

Add a pattern

Protect your investment now

You invest time and money to build your sending reputation with the major ISPs. Don’t leave all that hard work to chance! Start protecting your goodwill using email suppression lists. Who knows, like Warren Buffett said, your reputation might last a good 20+ years!

Do you have any special automations for treating blocklisted recipients in your workflow? Share in the comments.

Šarūnas Ročevas
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