Why do emails bounce?

A bounce is an email that came back. The receiving mail server refused it, and your sending service passed the refusal on to us.

There are two kinds, and they mean different things.

Permanent bounces

The address doesn't exist. Someone mistyped it when they signed up, or they left the company and the mailbox was closed, or the whole domain is gone. Sending to it again will never work. GoodPostal stops emailing a permanently bounced address after the first bounce, automatically, and marks the contact “Not emailable”. You don't have to do anything. Keeping the contact is fine; if the person gives you a new address, they can subscribe again.

Temporary bounces

The address exists, but the mail couldn't be delivered right now. The mailbox is full, or the receiving server was busy or briefly down. GoodPostal retries on your next campaign. If the same address fails three times in a row with no successful delivery in between, we stop and mark it “Not emailable” too.

Why bounces matter more than they look

Every email sending service watches your bounce rate. A high rate tells them you're sending to a list you didn't build carefully, and they protect their own reputation by pausing yours. Amazon SES puts an account under review at 50 bounces per 1,000 emails. Mailgun and SMTP2GO draw the line at the same 50. Postmark at 100. Watchdog shows your number next to your service's line.

Where bounces come from

Old lists are the usual cause. A list that hasn't been emailed in a year or two has addresses that quietly died in the meantime, and the first campaign to it finds them all at once. Imported lists from another platform carry whatever that platform never cleaned. Typos at signup are the rest.

What to do about them

Nothing about the addresses themselves: a dead mailbox can't be repaired. Send your next campaign only to people who opened something in the last six months, then widen from there. Before importing an old list, expect bounces from it and send to it in smaller batches. When you import a CSV, GoodPostal flags obvious typos like gamil.com in the error report so you can fix them before they bounce.

Next: why spam reports happen, the other number your sending service watches.