Reading the bounce log

A bounce is a message the receiving server did not accept. The 2Mail dashboard shows every bounce per sending domain, together with the recipient's reply. Once you learn to read that log, you see within a minute whether the problem sits with one address, with one receiving party or with your own domain.

Step 1: open the log

Open your sending domain in the dashboard and go to the delivery log. Filter on bounces and rejections. Each line shows the recipient address, the time, the status and the literal reply of the receiving server.

Step 2: hard or soft?

• Hard bounce — the recipient refuses for good. The address does not exist, the domain does not exist, or the recipient explicitly blocks you. The status code starts with a 5. 2Mail unsubscribes that address automatically; do not try it again.
• Soft bounce — a temporary problem: the mailbox is full, the receiving server is briefly unreachable, or it asks you to come back later (greylisting). The status code starts with a 4. Our relay retries automatically; you need do nothing unless it keeps going.

Step 3: read the reason

The reply of the receiving server usually says literally what is wrong. A few common ones:

• User unknown or no such user — a typo in the address or an employee who left. Correct or remove the address.
• Mailbox full — temporary; if it lasts for weeks, the mailbox is abandoned.
• Greylisted or try again later — normal on first contact; the retry sorts it out.
• Spam, policy or blocked — the recipient finds the message or the sender suspicious. Look at your SPF and DKIM status and at the content of the message.

Step 4: recognise patterns

One bounce means nothing. Look at the pattern:

• Many bounces at one receiving party, for instance all addresses at one large mail provider — that party is throttling you. Check authentication and temporarily lower the volume to that party.
• Bounces spread across all recipients after a list import — the list is stale. Clean it before you send further.
• Suddenly many bounces on one day — a template with a wrong link or attachment, or a campaign to an old list.

What 2Mail does by itself

Bounces are handled automatically: hard bounces are unsubscribed, soft bounces retried and greylisting resolved with a retry. If you want the bounce events in your own system, you can also receive them as a webhook.

Why bounces hurt your reputation and how to keep them low is explained on email deliverability.

Still stuck?

Copy the log line you do not understand, with its time, into contact. We translate the recipient's reply and tell you what you can do.