Soft bounce
A delivery failure that may clear up on its own, such as a full mailbox or a temporarily unavailable server, as opposed to an address that does not exist.
What it means
There is no standard definition, and platforms draw the line differently. Postmark describes a soft bounce as a temporary failure to deliver, giving a full mailbox, a disabled account and an exceeded quota as examples. A full mailbox can be reported with a temporary 452 4.2.2 or a permanent 552 5.2.2, and Postmark, for one, still counts a full mailbox as a soft bounce because the address itself exists.
A single soft bounce needs no action. Repeated soft bounces to the same address over weeks are a different matter: Gmail, for one, returns 552 5.2.2 for a mailbox that is full and inactive, and suppressing an address after several consecutive soft bounces is a sensible rule. Amazon SES does not count failures such as a full mailbox toward its bounce rate, and Bird does not suppress addresses for soft bounces.
Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- Postmark API: Bounce typespostmarkapp.com
- RFC 3463, section 3.3: Mailbox Statusrfc-editor.org
- Google Workspace Admin Help: Gmail SMTP errors and codesknowledge.workspace.google.com
- Amazon SES Developer Guide: Enforcement FAQs (bounce rate)docs.aws.amazon.com
- Bird Docs: Why did my email bounce?bird.com
All 432 terms in the glossaryThe wiki: blocklists and bounce codes