Do all bounces mean invalid addresses?

Got a bounce notification and wondering if you should delete that contact forever? Not so fast. A bounce just means the email didn't deliver right now. That doesn't always mean the address is gone for good.

There are two very different kinds of bounces, and mixing them up is where people get into trouble.

Hard bounces are permanent failures. The address doesn't exist, the domain is gone, or the receiving server has outright rejected you. These you act on immediately. Remove them from your active list and don't retry.

Soft bounces are temporary. The address is real, but something got in the way. Common soft bounce causes include a full mailbox, a server that's temporarily down, rate limiting from the receiving end, or even greylisting (where the server intentionally delays unfamiliar senders). The address isn't bad. The timing just wasn't right.

So how long do you retry a soft bounce? Most ESPs handle retries automatically for 24 to 72 hours after the first attempt. If delivery succeeds in that window, great. If it doesn't, the message expires. That's normal, and it doesn't mean the address is dead.

The "soft bounce becoming hard" thing is a policy decision, not a technical one. Most senders set a threshold, something like three to five consecutive soft bounces across multiple send cycles, before treating an address as invalid. Your ESP probably has a default threshold already. It's worth knowing what that number is.

Here's where it gets practical. If you suppress every bounce immediately, you'll quietly remove valid addresses from people who just had a full inbox that week. If you ignore all bounces, your sender reputation takes a hit because you're repeatedly hitting bad addresses. Neither extreme works.

A sensible approach looks like this:

• Hard bounce on the first instance? Remove it.
• Soft bounce? Let your ESP retry automatically. Don't manually intervene yet.
• Soft bouncing repeatedly across three or more campaigns? Move it to a watch list or remove it. It's not behaving like a live address anymore.
• Reputation-based rejections (where the server rejects you, not the address)? That's a different problem worth investigating separately. The address may be fine. Your sending reputation might not be.

If you're unsure how your current setup handles bounce thresholds, it's worth digging into your ESP's bounce settings. And if your list has a lot of unknowns, it might be time for a clean. We do that if you want a second pair of eyes on it.