What is the Email Suppression List?


An email suppression list helps prevent your outbound email server from getting listed as a spammer. It is a list of email addresses from which you received bounce or block error messages when sending email to them. If an email address is currently on the email suppression list and you send them a new email, we block sending to that address. This helps prevent the sending mail server from being listed as a spam address due to repeated bounce errors. 

Front only maintains a suppression list for our generic SMTP forwarding email channels, which we use Sendgrid to send emails with. This article doesn't apply to Gmail, Office 365, or Custom SMTP channels.


Step 1

If you send an email that bounces, Front will initially display the error message received from the recipient's email server. It may take some time to be placed on the suppression list depending on the nature of the error:


Step 2

Once Sendgrid adds the recipient's address to the list, the initial error message is replaced with the one below:


Step 3

Clicking on the Remove link displays this pop-up:


Step 4

Click the red Remove button. If removal succeeds, you should see this notification:

Step 5

The original error message will reappear in the conversation's activities. You will need to resend the message once the address is removed.


I received an error that I've already removed the email from the list- what does this mean?

If you remove an address from the suppression list and get a bounce error again within 6 months, you'll see this message if you try to remove the address:


The reason for this is that repeatedly removing the block and trying to send again defeats the purpose of a suppression list and will reduce your sending reputation.  It also indicates that an issue persists with that recipient.  If this happens, we recommend reaching out to the recipient through a different channel of communication to determine the reason for the block.

Why is the recipient on the list?

There can be many specific reasons that your recipient is on the suppression list, but they're all related to errors received when communicating with the recipient's mail server.  For example:

  • Your team is sending too many emails to a single domain.

  • The domain's email server is down.

  • The recipient's inbox is full/over-quota.

  • The content sent is detected as spam.

  • Attachments are too large for the recipient's email server.

Can you share all addresses on the list?

No. The nature of the suppression list means we can't provide the content of the list.  We can only query individual addresses as sending errors occur. 

How long do addresses stay on the list?

Email addresses will be listed for various amounts of time on the suppression list. Some listings are short lived (minutes to hours), other listings are more long term, and some are permanent failures. This depends on the type of rejection the recipient's mail server returns. 

If there are multiple recipients, will recipients not on the suppression list receive the message?

Yes. If you send a message to multiple recipients and one is on the suppression list, all non-suppression list recipients will receive the message. The message is only blocked for the recipient on the suppression list.