What does “domain not found” mean?
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Your campaign bounced a few emails with 'domain not found.' That message is straightforward, but the diagnosis isn't always obvious.
'Domain not found' means the DNS lookup for the email domain failed. When your mail server tried to look up the domain part of the email address (the part after @), the DNS system came back empty. That's a permanent failure. There's nowhere to deliver the message.
Why it happens: The domain was never registered. Or it was registered once but the registration expired. Or the domain exists but has no MX records (the records that tell the internet 'this is where email goes'). Rarely, it's a temporary DNS propagation delay if they just moved mail servers.
What the codes look like: You'll typically see SMTP code 550 or 553, often with text saying 'domain not found' or 'no such domain.' The enhanced code 5.1.2 means 'bad destination domain.'
How to fix it: First, verify the email addresses are spelled correctly. Then check if those domains actually have MX records. You can use a free DNS lookup tool like MXToolbox to pull up the MX records and see if they exist.
If the domain's MX records look good but you're still bouncing, the problem might be on your end. Check your DNS configuration, SPF record, and DKIM setup. If the domain is genuinely invalid and you've confirmed it, suppress those addresses. No point continuing to bang on a door that doesn't exist.
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