Invalid addresses, bounces and unsubscribes

You do not have to prune your lists by hand. Three separate mechanisms remove addresses from sending automatically, and together they explain most cases of "why did fewer people get this than my list says?".

Invalid addresses

Every address is validated when it is imported. Ones that cannot receive mail are marked invalid and excluded from every campaign and automation from then on. They stay visible on your Contacts page — they are skipped, not deleted.

Bounces and complaints

When a message hard-bounces, or a recipient marks it as spam, that address is added to your suppression list automatically. It will not be sent to again.

This matters more than it sounds: mailbox providers judge you on how often you send to addresses that do not exist, so continuing to mail a bounced address damages delivery for everyone else on your list.

Unsubscribes

Unsubscribes are captured and suppressed automatically too. An unsubscribed contact stays in your audience but stops receiving mail, and re-importing them from a CSV does not undo it.

Why your recipient count is lower than your list size

Your audience shows how many contacts it holds. The number actually mailed is that figure minus everyone invalid, bounced, complained or unsubscribed. A gap is normal and healthy — it is the system protecting your sending reputation.

A very large gap on a freshly imported list usually means the list was old or bought, and it is worth pausing before sending to it at scale.

Next: open Contacts and filter by Source to see which import a problem list came from.