Bounce Processing

Bounce processing is an essential practice for mailing list.

Sometimes a subscriber's email account is full, or the email account no longer exists, or their domain's email hosting has been moved or cancelled entirely. In all of these cases the receiving mail server will bounce incoming mail, and the expectation is that email senders will eventually stop sending mail to this address. Violating this expectation can result in your list domain or entire mailing list server ending up on a blocklist - either with that specific provider or a public blocklist used by multiple providers.

However, sometimes this issue is temporary and will eventually be resolved. This is why mailing list applications generally won't immediately unsubscribe an address after a single bounce. Additionally, there are options to temporarily pause delivery to an address that is bouncing - a middle ground between unsubscription and ignoring bounce messages.

In Harmony mailing lists, these settings are found under "Settings" and "Bounces". The "Number of notices before removal" and "Number of days between each disabled notification" are the settings to focus on, and you can see the suggested settings in the screenshot below.