2 min read
Hard Bounces vs. Soft Bounces: Reading the Signals
Not every bounce means the same thing. Telling a permanent failure apart from a temporary one — and reacting correctly to each — is one of the simplest ways to protect your sending reputation.
On this page
When an email can't be delivered, the receiving server sends back a bounce. But bounces aren't all created equal, and treating them the same way is a quiet reputation killer.
Hard bounces: permanent failures
A hard bounce means the address will never accept mail. The mailbox doesn't exist, the domain is invalid, or the server has flatly rejected you. The defining feature is that retrying won't help — the answer is a permanent "no."
The correct response to a hard bounce is to stop sending to that address immediately. Continuing to hammer a dead address tells mailbox providers you're not maintaining your list, which is exactly the behavior spammers exhibit. This is why suppression lists exist: once an address hard-bounces, it should be automatically suppressed so you never send to it again.
Soft bounces: temporary failures
A soft bounce means "not right now." The mailbox is full, the server is temporarily overloaded, the message was too large, or the receiver is greylisting you (deliberately deferring a first attempt to see if you retry like a legitimate sender would). These are transient, and a well-behaved sending system retries them on a sensible schedule.
The nuance: a soft bounce that never resolves eventually becomes a hard bounce. If an address soft-bounces repeatedly over days, it's effectively dead, and most systems will promote it to a permanent failure and suppress it.
Why the distinction matters for reputation
Your bounce rate is one of the signals mailbox providers use to judge you. A high hard-bounce rate is especially damaging because it signals a stale or purchased list. Keeping that rate low — by suppressing dead addresses promptly and only collecting addresses through genuine opt-in — is one of the highest-leverage things you can do.
Seeing it in practice
In Buzzmark, each hive's delivery events record the bounce type and the reason the receiving server gave, so you can tell a full mailbox apart from a hard rejection at a glance. Hard bounces feed the suppression list automatically, and you can inspect suppressions any time to understand why an address is being skipped.
The short version: retry soft bounces, suppress hard bounces, and never argue with a permanent failure. Your reputation will thank you.
Send transactional email that lands - from the EU
A clean API and SMTP relay with tracking, inbound mail and webhooks. Free up to 300 emails a month, no card needed.
Keep reading
Engineering 5 min read
Buzzmark Is Opening a Second Sending Location in the Netherlands
Today every message Buzzmark delivers leaves from our servers in Spain. In December 2026 we're adding a second sending l...
Deliverability 4 min read
We've doubled our sending infrastructure in Spain
Over the past few weeks we doubled the size of the infrastructure that delivers your mail. Nothing changes on your side....
4 min read
How Inbound Email Works in Buzzmark: MX Records, Forwarding, and Webhooks
Buzzmark does not just send. Point an MX record at us and we will receive mail for your domain, then forward it to your...