April 10, 2026
Hard Bounce vs Soft Bounce: What's the Difference?
Not all bounces are equal. Learn the difference between hard and soft bounces, why they matter for your sender reputation, and how to handle each one.
When an email fails to reach its destination, the sending server receives a bounce message. But not all bounces mean the same thing - and treating them the same way can seriously damage your deliverability.
What is a hard bounce?
A hard bounce is a permanent delivery failure. The email cannot be delivered and never will be, no matter how many times you retry. Common causes:
- The email address does not exist (
550 User unknown) - The domain has no MX records and cannot receive emails
- The recipient's mail server has permanently blocked your address
What to do: Remove hard bounces from your list immediately. Keeping them will increase your bounce rate, which ISPs use as a signal of poor list quality.
What is a soft bounce?
A soft bounce is a temporary delivery failure. The email address is valid, but delivery failed for a transient reason:
- The recipient's mailbox is full
- The receiving server is temporarily unavailable
- Your message was too large
- Greylisting (the server asks you to retry later)
What to do: Most email platforms retry soft bounces automatically for 72 hours. If a soft bounce persists over multiple campaigns, treat it like a hard bounce and remove it.
Why the distinction matters
ISPs track your bounce rate closely. A bounce rate above 2% is generally considered a warning sign. Above 5%, you risk being throttled or blacklisted.
Hard bounces are the most damaging because they signal you're sending to addresses you haven't validated - either because you bought a list, scraped emails, or stopped cleaning your database.
How to prevent bounces before they happen
The most effective approach is to verify emails at the point of entry, before they enter your database:
- Validate format with a syntax check (
regex) - Confirm the domain can receive email with an MX record check
- Verify the mailbox exists with an SMTP check
This removes the root cause rather than cleaning up after the fact.
Check your emails now
Use MailTruster's free email verification tool to check any address for syntax, MX records, and SMTP deliverability before adding it to your list.