What probing is
Some mail servers say yes to every address, so for those a real one-line email checks the mailbox: delivered means it's real, and a bounce keeps it out.
Before an address can join a campaign, it's checked. Most mail servers will say whether a mailbox exists, but some say yes to everything. For those, a real email does the asking. That's a probe.
Every address is checked first
| The check | What it asks |
|---|---|
| Its domain | Does it take email at all? |
| Its mail server | Does it know this mailbox? |
| A probe | Only when the server can't say |
The answer is kept. The address isn't checked from scratch next time, on this list or any other.
Some servers say yes to everything
A catch-all mail server answers yes to every address. A real person: yes. A typo: yes. Someone who never existed: yes. So asking it proves nothing.
Those addresses aren't blacklisted. They're probed, and mailed only once the probe confirms them.
A real email gets the real answer
The probe is a real, one-line email called a mailbox check.
- If it's delivered, the address is real.
- If it bounces, the address never reaches your campaign.
A list's Clean tab counts the addresses still waiting on a probe: Why every list is cleaned shows where.
Probes stay apart from your sending
- Probes go out from their own mail server.
- They use their own domains, taking turns across them.
- They keep a steady pace for each mailbox provider.
They run apart from your campaigns.
Why it's worth it
Every bounce tells the mailbox providers a list is out of date, and they remember. Probing keeps those addresses out, so you get fewer bounces, a cleaner sending record, and more of your mail in the inbox.