When No Más Rebotes marks an address Deliverable, its mail server confirmed during our email verification check that the mailbox exists and accepts mail. That prevents most bounces. But sending is a separate event, at a different time, from a different sender. So a small share of Deliverable addresses can still bounce for reasons unrelated to the address itself.
If a server doesn’t answer the first time, we try again during our check. This happens with greylisting (a server temporarily refusing unknown senders to filter spam) or when a security filter such as Mimecast holds the connection. Your sending platform may not retry the same way, or the server may have been down when your campaign went out. In one customer campaign we reviewed, about a quarter of the bounces came from servers that were unreachable at send time, not from bad addresses.
Common reasons for a Deliverable email address to bounce
The address has a problem
- The mailbox changed after we checked it. People leave jobs and providers close inactive accounts.
- The address forwards to a mailbox that’s closed. The bounce comes from a different domain from the one you sent to.
- The domain stopped receiving email. The company may have moved its email or closed.
Something temporary got in the way
- Temporary problems. A full mailbox, a server outage or throttling at send time can cause a bounce that often clears on a later attempt.
- Greylisting. The server turned away the first attempt from an unfamiliar sender. Most platforms retry and the email arrives after a short delay, but some record the first rejection as a bounce.
Something about the sender or the message
- Your sending domain or IP is blocked. The recipient may accept our check but reject mail from a sender with a poor reputation or on a blocklist.
- Authentication problems. Missing or misconfigured SPF, DKIM or DMARC can cause rejections even at valid mailboxes.
- Security filters. Corporate filters can accept the connection, then reject or quarantine the message because of its content, links, attachments or volume.
- Sending too fast. Large bursts to one domain can trigger rate limits.
It wasn’t really a bounce
- Platforms label bounces differently. Some platforms record an email as bounced when their own rules stopped it from going out. For example, the address bounced or unsubscribed in the past, it’s on a suppression list, or the send broke a platform limit. No receiving server rejected the email.
- Auto-replies counted as bounces. Some platforms record out-of-office and similar automatic replies as soft bounces, even though the email was delivered.
To find the exact cause of your bounce, look up its bounce message or code in our bounce code guide. It tells you whether the address, your sending setup or the email is the problem, and what to do next.
What should I do when a Deliverable address bounces?
- Start with the bounce message, not the hard or soft label your platform gives it.
- Look up the message in the bounce code guide. It tells you whether the address, your sending setup or the email itself is the problem.
- Check when you sent. If you sent the email more than a few days after verifying, the mailbox may have closed since. Re-verify older lists before sending.
- If it’s a temporary (4xx) code, check how long your sending platform keeps retrying before it records a bounce, and send again later.
- If it points to your sending setup, send one plain email to the address from a different account, such as a personal Gmail. If it doesn’t bounce, the address is fine and the problem is your sending setup.
How can I avoid unexpected bounces?
- Send soon after verifying. Log in and verify your list before you send.
- Spread large sends to one domain over time.
- For a very low bounce rate, download only Deliverable emails.
Does No Más Rebotes guarantee that verified addresses won’t bounce?
No verification service can promise zero bounces.
A Deliverable result means the mailbox existed and accepted mail when we checked. We check each address thoroughly, but mailboxes get closed, servers go down, and receiving systems judge the sender as well as the address.
Still have questions? Contact us.