Soft bounce
A temporary failure — full mailbox, downtime, or greylisting. May succeed later; rules differ by ESP.
Say it out loud
“A temporary failure. The platform retries, and after enough of them it gives up on the address.”
A soft bounce means the problem is temporary: mailbox full, server busy, greylisting. Platforms retry on their own schedules, and after some number of consecutive failures most convert the address to suppressed. There is no universal threshold — each platform documents its own, and they genuinely differ.
Five consecutive soft bounces to the same address is not a busy server. It is an abandoned mailbox that will become a recycled spam trap.
Every platform sets its own conversion threshold.
There is no industry "seven soft bounces" rule.
It is repeated constantly and it is not a standard. Read your own platform's documentation.
Your platform
Klaviyo, Mailchimp and friends do this automatically.
What goes wrong
Assuming your platform's threshold matches the one from your last job. They differ, and a migration is exactly when a quietly decaying segment gets carried across intact.
The dated rule behind this
A definition is not a citation. These are the pages with the primary source, the date it was published, and what to do about it.
See also
Where this sits
Stop 6, the verdict lands. The message goes to an inbox, a spam folder, a refusal, or an address that was never a person.