How to interpret bounce-rate thresholds by list type?

Bounce rate means something different depending on who's on your list and where those addresses came from. A threshold that signals a serious problem on a fresh opt-in list might be normal for a five-year-old imported database. The context changes the interpretation.

What hard bounce rate is measuring

Hard bounces are permanent delivery failures: addresses that don't exist, domains that have stopped resolving, or accounts that have been shut down. Every hard bounce is a signal about your data quality. High hard bounce rates tell mailbox providers and blocklists that you're sending to addresses you shouldn't have, which damages your sender reputation regardless of how good your content is.

Thresholds by list type

Fresh opt-in lists (double opt-in especially). Hard bounce rate should be well under 0.5%. These lists are recent, permission-based, and verified. If you're seeing above 1% on a fresh double opt-in list, something is wrong with your signup validation or address handling.

Single opt-in or older opt-in lists. Under 1% is healthy. Between 1% and 2% is a warning. Above 2% means real hygiene work is needed before your next send.

Imported or legacy lists (haven't been sent to in over a year). Bounce rates of 3-5% are common because email addresses have a natural churn rate of 20-30% per year. An address that was valid two years ago may not be valid now. Anything above 5% on an imported list is high enough that it could trigger ESP account review.

Purchased lists. Don't use them. Ever. Bounce rates on purchased lists frequently exceed 20-30%, they contain spam traps, and no legitimate list vendor can tell you what percentage of addresses are current. The deliverability damage isn't worth whatever they cost.

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