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What is an email bounce rate?

Also called: hard bounce, soft bounce, email bounce, Zero-Bounce Deliverability Benchmark

Bounce rate is the share of sent emails that were returned as undeliverable. Hard bounces are permanent failures, such as an address that doesn't exist; soft bounces are temporary, such as a full mailbox or a server that is briefly unavailable.

By John Britton, VP of Marketing, MedicalProspects · Updated November 4, 2026 · Email & Deliverability

Why it matters for healthcare sales and marketing

Mailbox providers read high bounce rates as a sign of a poor-quality or purchased-and-unverified list. That damages your sender reputation, so later emails, even to good addresses, are more likely to land in spam. Email service providers also monitor bounces and can suspend accounts that bounce too much.

How it works

  • Hard bounce: permanent. The address or domain doesn't exist, or the server rejects it outright. Remove hard-bounced addresses immediately and never mail them again.
  • Soft bounce: temporary. The mailbox is full, the message is too large, or the server is down. Retry a few times; if it keeps soft-bouncing, treat it as bad.
  • Bounce rate = bounced emails divided by emails sent. Track hard and soft bounces separately.

The main levers are verifying addresses close to the send, removing old records, and warming up new sending domains gradually.

Comparison of hard bounces (address doesn't exist, domain doesn't exist, rejected by server; remove immediately) and soft bounces (mailbox full, message too large, server temporarily down; retry, then remove if repeated).
Hard bounces are permanent and should be removed at once. Soft bounces are temporary and can be retried.

Example

Illustrative scenario. A team sends to a list it hasn't touched in a year and sees hard bounces several times higher than usual. It pauses the campaign, re-verifies the remaining addresses, removes failures and restarts in smaller batches. Bounces return to normal and later campaigns reach the inbox again.

Common mistakes

  • Retrying hard bounces. They won't succeed, and each attempt hurts your reputation.
  • Looking only at averages. One bad segment can hide inside a good overall rate. Check bounces by list and source.
  • Sending a big list from a new domain. Warm up gradually so mailbox providers learn to trust you.
  • Not suppressing bounced addresses across tools. Share your suppression list between your CRM, marketing automation and sales engagement tools.

How MedicalProspects does it

MedicalProspects verifies emails before every delivery and replaces hard bounces one-for-one under its 99% deliverability guarantee. The house phrase "zero-bounce benchmark" describes the same goal: keep hard bounces as close to zero as possible.

Related terms

  • Email VerificationEmail verification is checking that an email address is correctly formed, belongs to a domain that accepts mail, and points to a mailbox that exists, before you send to it. For healthcare lists it also means confirming the address still belongs to the right person in the right role.
  • SMTP Email VerificationSMTP email verification checks whether a mail server will accept a specific address, by opening a connection to the server and asking about the mailbox without sending a message.
  • Deliverability GuaranteeA deliverability guarantee is a data provider's promise that a stated share of the emails it supplies will not hard-bounce, usually backed by replacing or crediting any addresses that do.
  • Data DecayData decay is the gradual loss of accuracy in a contact database as people change jobs, retire, move practices, or their organizations merge and change email domains.
  • Sender ReputationSender reputation is how mailbox providers such as Gmail and Outlook judge the trustworthiness of your sending domain and IP addresses, based on signals like spam complaints, bounces, spam trap hits, engagement and authentication.

Put it to work

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