Bounces, and why they matter so much

A bounce is a mailbox provider refusing your message. There are two kinds and they are treated differently.

Hard bounces

The address does not exist, or the domain does not. This will never succeed, so the address is added to your suppression list automatically and not tried again.

Hard bounces are the ones that damage you. Mailbox providers read a sender who repeatedly mails non-existent addresses as someone working from a bought or scraped list, because that is usually what it means.

Soft bounces

A temporary refusal — the mailbox is full, or the server is busy. These are not permanent and do not immediately suppress the address.

The numbers that stop a campaign

• Above 2% is a warning sign.
• At 4% a campaign is stopped for review.

For scale: 4% is 40 bad addresses in a thousand. A healthy list sits well under 1%, so reaching 4% is not bad luck — it says something about where the list came from.

Mailbox providers apply their own thresholds too, and theirs are not published. By the time you can see a problem in your own numbers, they have usually already acted.

What to do about a high bounce rate

Do not simply resume and continue. See Why is my campaign paused?.

• Where did the list come from? Bought, scraped and very old lists are the usual answer, and no amount of careful sending fixes a list of addresses that do not exist.
• How old is it? Addresses decay — people change jobs. A list untouched for two years will bounce heavily however good it was.
• Send to your recent, engaged contacts first and rebuild from there.

What you do not have to do

Prune by hand. Bounces are suppressed automatically as they happen — see The suppression list.

Next: open Suppressions and look at the Reason column to see how much of your list has bounced.