Soft Bounce
A soft bounce is a temporary delivery failure where the receiving mail server rejects the message with a 4xx SMTP code. Causes include full mailbox, message size limits, receiver throttling, temporary DNS issues, and policy holds. Most sending platforms retry soft bounces for 24 to 72 hours before giving up.
SMTP responses in the 4xx range are soft bounces. Common ones: 421 (try again later), 450 (mailbox unavailable, temporary), 451 (local error, try later), 452 (insufficient storage). The receiver is saying try again, not no.
How sending platforms handle soft bounces
Modern senders retry with exponential backoff for 24 to 72 hours. After the retry window, the message is dropped and recorded as a permanent failure. Cold-outbound tools typically suppress an address after two or three consecutive soft bounces because sustained soft-bounce attempts hurt sender reputation.
What to do with soft-bounced addresses
A single soft bounce is usually noise. Persistent soft bounces (three or more on the same address) should be suppressed for at least two weeks. Bulk-importing a list with high soft-bounce rate on first send is a sign of stale or unverified data and a deliverability risk.
Frequently asked questions
Should I retry soft bounces manually?+
No. The sending platform retries automatically. Manual retries skip the backoff and hurt sender reputation.
Does Outsolvi track bounces?+
Outsolvi tracks opens and clicks via pixels and link wrappers, which fire only on delivered mail. Bounce information lives in the sending platform's reporting.
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