InboxReadyCheck

The process, in plain sight

A small conversation.
No email sent.

We open an ordinary email delivery conversation and end it before any message could be submitted.

The SMTP conversation

InboxReadyCheck connects to the receiving mail server on port 25 and asks about a recipient address. A typical exchange; real servers word their replies differently:

server  220 mx.example.com ESMTP
us      EHLO probe.inboxreadycheck.com
server  250 mx.example.com
us      MAIL FROM:<verify@inboxreadycheck.com>
server  250 OK
us      RCPT TO:<someone@example.com>
server  250 OK              <- there is a mailbox
us      QUIT

Where it stops matters.

We never send the DATA command, which is what starts a message. No message body is ever submitted or delivered.

Only after a server has accepted a real address do we also ask about one that cannot exist, beginning catchall-check-, and at most once per domain every 90 days. If the server accepts that too, it accepts every address (a “catch-all”), and its answer about a real address proves nothing either way.

What the answers mean

Valid

Accepted

The server accepted the mailbox, and does not accept everything.

Invalid

Rejected

The server said there is no such mailbox, or the domain cannot receive mail. The customer’s campaign does not email it, and it goes on that customer’s do-not-email list.

Risky

Unprovable

A catch-all server, or a provider that never says either way. Probably deliverable, but not proven.

Could not be checked

No answer

The server refused us, did not answer in time, or asked us to try later. A verified campaign does not email these addresses.

Our operating limits

  1. One list at a time. FullArc verifies one list at a time, across all of its customers.

  2. Slow by default. One address per connection, at least 30 seconds between connections, and never the same domain twice within five minutes.

  3. A daily ceiling that starts small. A new probe name starts at 50 connections a day and rises over two months, never past 12,000 a day.

  4. Answers are reused. A definite answer is kept for 30 days, so the same address is not asked about again, whichever customer asks. When a customer’s message to an address is delivered, that confirms it and we do not ask.

  5. New domains are left alone. We never check addresses at a domain registered in the last six months.

  6. Refusals are respected. After a refusal or a timeout we wait at least a day before asking about that address again. When a server asks us to try later, we wait at least 30 minutes, as asked.

  7. We stop ourselves. All checking halts, for every customer, until a person reviews it: when a server’s reply names a blocklist, after five refusals in a row, when our own name or IP address is listed, or when a list turns out to be mostly addresses that do not exist.

  8. Opt-outs are absolute. An opted-out domain or mail host is answered for without connecting to it.

Where addresses come from

FullArc customers check their own contact lists before an email campaign. This service does not collect, buy, generate, guess or sell email addresses.

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