Email bounce rate

A bounce is an email the receiving server refused to deliver. Bounce rate is the number of bounces divided by the number of emails you sent.

Bounce rate = (bounced emails ÷ sent emails) × 100

Sent: 10,000   Bounced: 150
Bounce rate = (150 ÷ 10,000) × 100 = 1.5%

Bounces come in two kinds, and each needs a different response.

After 3 to 5 consecutive soft bounces across several campaigns, treat the address as a hard bounce and remove it.

Every bounce comes with an SMTP code. Codes starting with 5 are permanent, codes starting with 4 are temporary.

Most bounces trace back to how addresses got on the list. Fix that and the rate follows.

• Use double opt-in

  A confirmation link proves the address is real, active and belongs to whoever signed up. It cuts bounces by 50 to 70%.

• Validate addresses on signup

  Check the format, confirm the domain has MX records, catch typos like gmial.com and block disposable addresses if you need to. Try it with the email verifier.

• Remove hard bounces immediately

  Automate it. Sending to dead addresses again tells providers your list is not maintained.

• Clean your list regularly

  15 to 20% of addresses go invalid every year. Remove or re-engage inactive subscribers every 6 to 12 months.

• Never buy lists

  Purchased lists carry 20 to 40% invalid addresses and no engagement. Build your list yourself.

• Watch repeat soft bounces

  Remove addresses after 3 to 5 consecutive soft bounces over multiple campaigns.

• Keep emails under 100KB

  Compress images, trim the code and link to large files instead of attaching them.

• Send consistently

  Gaps of 3 months or more let addresses go stale and subscribers forget you.

• Lower sender reputation

  Providers read a high bounce rate as careless sending, so more of your mail goes to spam. See sender reputation.

• Spam trap hits

  Abandoned addresses can be recycled as spam traps, and hitting them can get you blocklisted.

• IP and domain blocklisting

  A rate that stays high can put your IP or domain on blocklists, which blocks delivery almost everywhere.

• Less trust in the rest

  When much of a list is invalid, providers trust your mail to the valid addresses less too.

What to track

• Overall bounce rate, with a target below 2%
• Hard and soft bounce rates separately, and how many soft bounces succeed on retry
• Bounce rate per campaign and over time
• Bounce reasons and error codes

What to automate

• Remove hard bounces immediately
• Retry soft bounces 3 to 5 times over 72 hours, then remove persistent ones
• Alert when the bounce rate passes your threshold, and send a weekly report
• Validate addresses at signup