What Counts as a Normal Bounce Rate

Hard and soft are not the same number

A hard bounce is permanent: the mailbox does not exist, the domain does not resolve, or the server refuses all mail for that address. Sending to it again wastes a send and signals list neglect. These addresses should be suppressed the first time, automatically.

A soft bounce is temporary: the mailbox is full, the server is busy, the message was too large, or a greylist asked you to try later. A soft bounce is not evidence of a bad address, and treating it as one removes people who would have received the next message.

The range, and why it exists

For a cold list, under two percent is healthy and under one percent is what a verified list looks like. Between two and five percent is a warning: the list is ageing, or a source is dirty, or you are re-sending to addresses that failed before. Above five percent, providers start asking questions, and suspension is a realistic outcome.

For an opted-in list the expectation is lower still, because double opt-in removes the dead addresses at signup. A newsletter bouncing four percent is not normal; it usually means a signup form that accepts anything, or a list that has not been cleaned in years.

• Under 1 percent: verified, clean, maintained.
• 1 to 2 percent: normal for a cold list with light verification.
• 2 to 5 percent: clean before the next send, and find the source.
• Above 5 percent: stop sending until the list is rebuilt or verified.
• Any hard bounce repeated: a suppression rule is missing.

Fixing it without guessing

Verify the list before sending rather than after. Syntax checks, domain and MX checks, and a mailbox-level probe remove dead addresses in that order of cost, and doing it once usually takes a cold list from five percent to under two. Keep the result and remove the invalid addresses permanently.

Then suppress. Every hard bounce should write to a suppression list that all mailboxes share, so the same address is not tried from a second sender next week. Without a shared list, ten mailboxes multiply one bad address into ten bounces.

Worked example: 8 percent that was really 1.5 percent

Agency reporting showed an eight percent bounce rate on a 12,000-address campaign, and the provider had already sent a warning. The agency was ready to rebuild the list. Splitting the report first showed that most of the bounces came from one server returning a temporary refusal on the first attempt, then accepting the retry.

After suppress-list cleanup and one retry pass, the true hard-bounce rate was 1.5 percent, which is ordinary for a cold list of that age. The eight percent figure had been produced by counting every failed attempt, including the ones that later delivered, as a bounce.

The change was in the reporting, not the list. From then on the report separated first-attempt failures from final failures, and the number stopped causing panics. The list still needed verification, but it did not need rebuilding.

Bounce type, what it means, and what to do

A rate is only meaningful alongside the split. Two percent of which the majority is soft is a very different list from two percent of which all is hard.

Bring the rate down before the next campaign

• 1Split last campaign's bounces into hard and soft in the report.
• 2Suppress every hard bounce across all mailboxes, not just the sender that produced it.
• 3Verify the unsent portion of the list before it goes out.
• 4Retry soft bounces once, then remove them.
• 5Find which source supplied the invalid addresses and stop using it unchanged.