What is Soft Bounce?
A soft bounce is a temporary email delivery failure caused by issues like a full mailbox, server downtime, or message size limits—the email may be delivered on retry.
A soft bounce means your email couldn't be delivered right now, but the address itself is valid. The receiving server returns a temporary failure code (4xx SMTP error), indicating the problem might resolve itself. Your email service will typically retry delivery for 24-72 hours before giving up.
Common causes of soft bounces include: • Recipient's mailbox is full (they haven't cleared old emails) • Recipient's mail server is temporarily down or overloaded • Your email is too large (attachments exceeding size limits) • Temporary spam filtering or greylisting delays • DNS or network issues between mail servers
Unlike hard bounces, soft bounces don't require immediate list removal. However, an address that repeatedly soft bounces over multiple sends should eventually be treated as problematic. Most ESPs track soft bounce patterns and convert persistent soft bounces to hard bounces after a threshold (typically 3-7 consecutive failures).
For transactional emails, soft bounces are particularly frustrating because time-sensitive messages like password resets may arrive too late to be useful.
Why Soft Bounce Matters
Soft bounces are normal and don't immediately harm your reputation, but patterns matter. A sudden spike in soft bounces might indicate your content is triggering spam filters, your IP reputation has dropped, or there's a technical issue with your sending infrastructure. Tracking soft bounces helps you catch deliverability problems before they become serious. For transactional emails, soft bounces mean delayed delivery—your user waiting for a password reset or verification code.
How Ark Handles Soft Bounce
Ark automatically retries soft-bounced emails with intelligent backoff—we don't hammer the receiving server but ensure your message gets through when possible. We track soft bounce patterns per address and automatically suppress addresses that repeatedly fail. Our webhooks notify you of soft bounces in real-time so you can handle time-sensitive failures in your application.
Frequently Asked Questions
How long will my email retry after a soft bounce?
Most email services retry for 24-72 hours with increasing delays between attempts (exponential backoff). Ark retries soft bounces for up to 72 hours. If the email still can't be delivered, it's marked as failed and you're notified via webhook.
Should I remove soft-bounced addresses from my list?
Not immediately. Track patterns instead. If an address soft bounces on 3-7 consecutive sends over multiple campaigns, consider removing it or moving it to a re-engagement segment. One-off soft bounces are normal and usually resolve.
Why am I seeing lots of soft bounces suddenly?
Common causes include: your content triggered spam filters (check for spammy words or broken links), your IP reputation dropped, the receiving mail server is having issues, or you're being rate-limited. Check if the bounces are concentrated on one domain or spread across many.
Can email size cause soft bounces?
Yes. Many mail servers reject messages over 10-25MB. If you're sending large attachments, they may soft bounce at some domains. Keep email sizes small—host large files elsewhere and link to them instead of attaching.
Is a full mailbox a hard or soft bounce?
A full mailbox is a soft bounce because the address is valid—the user just needs to delete some emails. However, a consistently full mailbox over months suggests an abandoned account that should eventually be removed from your list.
Related Terms
Hard Bounce
A hard bounce is a permanent email delivery failure that occurs when the recipient address is invali...
Bounce Rate
Email bounce rate is the percentage of emails that couldn't be delivered to recipients, categorized ...
Email Deliverability
Email deliverability is the ability to successfully deliver emails to recipients' inboxes rather tha...
Greylisting
Greylisting is a spam prevention technique that temporarily rejects emails from unknown senders, exp...
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