When to Remove an Address That Keeps Soft Bouncing: Counting Repeat Soft Bounces Across Sends

Count, for each address, how many different sends it soft-bounced in, and whether it was delivered after the last one. Suppress addresses with soft bounces in several sends (3 is a sensible default) and no delivery since; keep everything else. Hard bounces anywhere in the history go straight to suppression.

The repeat soft bounce finder does the count from a bounce or activity export in your browser. Sources, read 2 November 2026: RFC 3463 for code classes and Mailchimp's soft vs. hard bounces.

Soft, hard and blocked

Code class	What it usually means	What to do
4.2.2, "mailbox full"	Mailbox over quota	Retry; count it
4.4.x, timed out, deferred	Server or network trouble	Retry; count it
4.7.x, policy, rate limited	The receiver is throttling or refusing your sender	Fix the sender side; don't blame the address
5.1.x, 5.2.x	Permanent: no such user, disabled, full and inactive	Suppress now

The last row matters: some servers return mailbox full as 5.2.2, and Gmail's 552 5.2.2 says the account is out of storage and inactive. For one code in detail, the bounce message analyzer explains it; for how retries work, see SMTP deferral vs bounce.

Step by step

1. Export several sends. Bounces or full activity for at least the last four or five campaigns: email, bounce type or reason, and the date or campaign name.
2. Collapse retries. Several soft bounces for the same send (same day or same campaign) count once.
3. Count distinct sends with a soft bounce per address.
4. Check for later deliveries. A delivered row after the last soft bounce means the mailbox came back; keep it.
5. Apply your threshold. At 3 sends with no delivery since, add to the suppression list. Mailchimp's own lines are looser (7 or 15); stricter means fewer sends to dead mailboxes.
6. Upload the suppression list to every platform you send from, so the address doesn't come back through an import. See cold email suppression lists for keeping one list across tools.

Before you remove a batch

If hundreds of addresses at one provider started soft-bouncing on the same day, it's probably not hundreds of full mailboxes; it's a 4.7.x throttle or block on your sender. Read the codes first. Removing good addresses because of a block on your side shrinks your list without fixing anything. Handling soft bounces covers retry timing, and hard bounce vs soft bounce the difference in detail.

Limits

The count only sees the sends in your export. Without a date or campaign column, retries of one send can look like several sends. And an address that soft-bounced once or twice may or may not still exist; the history can't tell you.

Where SimpleVerifier fits

For the addresses that soft-bounced only once or twice, don't wait for more bounces: upload them at /verify to see whether each mailbox still exists, and drop the invalid ones before the next send. The first 100 checks are free with a Google sign-in. Pro is $39 a month with the first 100,000 checks a month at full speed, then slower, never cut off. See pricing.