How to Find Out Why an Email Bounced (and What to Do About It)
·2 min read
You send an email and moments later a message lands in your inbox saying it couldn't be delivered. It's confusing, and it can look alarming. If you're asking "why did my email bounce?", the answer is nearly always in the notice itself. Here's how to read it.
What is a bounce?
A bounce is an email that didn't reach its destination and was sent back to you. In everyday terms, it hit a dead end.
Step 1: Read the bounce message
Look for a short code and a line of text. Codes starting with 5 usually mean a permanent problem. Codes starting with 4 usually mean a temporary one.
The most common causes
The address doesn't exist. The most common reason. Either there's a typo, or the person left and the mailbox was closed.
The domain is wrong. Something like "gmial.com" or a company that no longer exists.
The inbox is full. A temporary problem. The address is real, but the person can't receive anything right now.
The receiving server is down or slow. Also temporary. Try again later.
The message was blocked. The receiving side decided your email looked unwanted, often because of the content, an attachment, or too many dead ends in your earlier sends.
The message is too large. Big attachments can be refused.
Step 2: Sort permanent from temporary
- Permanent: stop sending to that address and remove it.
- Temporary: try again once or twice over a few days. If it keeps failing, treat it as permanent.
Step 3: Check for typos
If it's a single important contact, look closely at the spelling and try again. Often the fix is one wrong letter.
Step 4: Look at the bigger picture
One bounce is normal. A lot of them is a sign your mailing list needs attention. If you send marketing emails, don't just fix one address at a time.
Step 5: Verify your list with VerifyFlow
Upload your list as a CSV or Excel file and VerifyFlow will flag addresses that don't exist, along with catch-all domains that can't be confirmed. It's a flat £20 per list, up to 1,000,000 rows, with no subscription.
Step 6: Prevent it from happening again
- Add a confirmation step when people sign up.
- Remove addresses that fail permanently.
- Re-verify your list before big campaigns.
Final thoughts
Understanding why an email bounced helps you fix it quickly. For one-off cases, read the notice and check the address. For ongoing email marketing, verify your mailing list with VerifyFlow so you spot dead ends before you send.