What is a Soft Bounce?
A soft bounce is a temporary email delivery failure where the recipient address exists but the message could not be delivered at that moment.
Soft Bounce Definition
A soft bounce occurs when an email is temporarily rejected by the recipient's mail server. The server returns a temporary failure code (typically a 4xx SMTP response), indicating that the address is valid but the message cannot be delivered right now. Most email service providers will automatically retry delivery several times over a period of hours or days before treating the message as permanently undeliverable.
The most common causes of soft bounces include a full recipient mailbox that has exceeded its storage quota, a recipient mail server that is temporarily offline or experiencing high load, a message that exceeds the size limit of the recipient server, DNS resolution issues that prevent the sending server from reaching the recipient server, and greylisting — a spam prevention technique where the server temporarily rejects messages from unknown senders and expects them to retry.
While a single soft bounce is not cause for alarm, repeated soft bounces to the same address over multiple campaigns can indicate a problem. If an address soft bounces consistently — typically three to five times across separate sends — it should be treated as potentially invalid and re-verified or removed from your list. Accumulating too many soft bounces can also impact your sender reputation, though the effect is less severe than hard bounces.
How Soft Bounces Relate to Email Verification
Email verification helps reduce soft bounces by identifying addresses that are likely to cause delivery issues. While verification cannot predict every temporary server outage, it can detect full mailboxes, inactive accounts, and domains with unreliable mail servers. Our verification service flags these addresses as "risky" or "accept-all," giving you the information needed to make informed sending decisions.
By regularly verifying your email list with Email Verifier by EcomTech, you can catch addresses that have become inactive or problematic since your last send. This proactive approach keeps your soft bounce rate low and your sender reputation strong, ensuring maximum inbox placement for your campaigns.
Reduce soft bounces and improve deliverability. Verify your email list to identify risky addresses before sending.
Try Email Verifier FreeSoft Bounce FAQ
A soft bounce is a temporary delivery failure — the email address exists but the message could not be delivered at that moment. A hard bounce is a permanent failure where the address does not exist or the domain is invalid. Soft bounces may succeed on retry, while hard bounces never will.
Common causes include a full recipient mailbox, a temporarily unavailable mail server, message size exceeding the recipient server limit, the recipient server being overloaded, or temporary DNS issues. Auto-reply and out-of-office messages can also be classified as soft bounces by some ESPs.
Not immediately. Soft bounces are temporary and the address may accept mail on the next attempt. However, if an address soft bounces consistently over multiple sends (typically 3 to 5 times), you should remove it or re-verify it using an email verification tool to confirm it is still valid.
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