What is a DNS-related bounce?
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You hit send, and instead of a delivery confirmation you get a bounce back saying something like "host not found" or "unable to route." That's a DNS-related bounce, and it means your sending server went looking for the recipient's domain in the internet's directory and came up empty-handed.
DNS (Domain Name System) is what connects a domain name like "example.com" to the actual servers that handle its email. When you send to captain@deepcurrent.io, your server first asks DNS a simple question: "Where do I deliver mail for deepcurrent.io?" If DNS can't answer, the email goes nowhere.
There are a few ways that lookup can fail. The domain might not exist at all, which gives you a hard bounce (permanent failure, code 550 "host not found" or 5.4.4 "unable to route"). The domain might exist but have no MX records configured, which tells the world it can't receive email. Or the DNS server itself might time out or throw a SERVFAIL error, which is a temporary failure (code 4.4.3) that usually resolves on its own.
The permanent vs. temporary distinction really matters here. A missing domain or missing MX record is a hard bounce. Treat every address at that domain as undeliverable and suppress it. A DNS timeout or server error is a soft bounce. Your ESP should retry automatically, and it often clears up within hours.
One thing that catches senders off guard: DNS failures can hit every single address at a domain at once. If deepcurrent.io's DNS goes down, all your emails to that domain fail together, not just one address. That can make a DNS issue look alarming in your bounce report when really it's one root cause.
Want to know what happens next? See what causes "host not found" for a deeper look at how to diagnose the specific error you're seeing.
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