Your Newsletter Bounced: How to Find Out Why

You sent a newsletter and your tool shows a bounce rate that is higher than usual. Before you change anything, find the cause. Different causes need different fixes, and the bounce message usually says which one you have.

Step 1: Separate hard from soft bounces

A hard bounce is permanent: the address does not exist or the domain is gone. A soft bounce is temporary: a full mailbox, a server that was busy or a message that was too large. Hard bounces get removed at once. Soft bounces get another try later and are removed if they keep failing.

Step 2: Read the codes

Each bounce comes with a code and a sentence. Codes starting with 5 are permanent, codes starting with 4 are temporary. The email error code guide explains the common ones, such as 550 5.1.1 (the mailbox does not exist) or 552 (the mailbox is full).

Step 3: Look for a pattern

• Mostly "user unknown": the list is old or contains typos. Verify it.
• Many bounces from one provider: a rule at that provider, or your message was blocked. Look at the text of the rejection.
• Messages about authentication or policy: your SPF, DKIM or DMARC records may be missing or wrong. Use the SPF, DKIM and DMARC checker.
• Messages about reputation or blocklists: reduce the volume, clean the list and check whether your domain or address is listed.

Step 4: Clean before you send again

If the bounces point to bad addresses, export the whole list and verify it on the bulk verification page. Remove the invalid addresses, send a first small batch to the valid ones and watch the numbers before the full send. Treat accept-all and risky addresses carefully, as the post on accept-all and risky results explains.

Step 5: Stop it from happening again

Verify new sign-ups before they reach your list, remove the addresses that bounce right after each send, and run a full clean before every large campaign. A routine is much cheaper than recovering from a damaged reputation.

What is a normal bounce rate? Well under two percent for a list that has been cleaned. If you see more than that regularly, the list or the setup needs attention.

Mistakes that make bounces worse

• Resending to the same list straight away. If the cause was bad addresses, a second send repeats the damage.
• Removing only the first few bounces. Remove every hard bounce, and track soft bounces that repeat.
• Blaming the subject line. Bounces happen before anyone sees the message. They point to addresses or setup, not to content.
• Never looking at the raw message. The text of the bounce often names the exact reason, such as a full mailbox or a policy block.

Questions people ask

How many bounces are too many? Many newsletter tools start to warn above a few percent, and mailbox providers pay attention to even smaller numbers on a regular basis. Aim for well below two percent on a cleaned list.

Are bounces the same as spam complaints? No. A bounce is a delivery failure. A complaint is a person marking your message as spam. Both matter, and complaints are usually even more serious.

Do I need to verify if only a few bounced? A few bounces on a small send are normal. If they come back each time, or if you have not cleaned the list in a long time, run a verification before the next campaign.

Keep the bounce report

Save the bounce report with the date of the send. Over a few campaigns it shows whether problems repeat on the same domains, which points to a cause you can fix rather than a one-off event.