A catch-all inbox that stops receiving does not announce itself. Signups keep succeeding, software keeps running, and the failure only surfaces later when verification links never arrive or accounts start dropping out of campaigns. The fix is a repeatable test you run on a schedule: send a message to a random local part from an outside provider, confirm it lands in POP3, then check the MX IP against major DNSBLs. That three-step loop catches both delivery failures and blacklist listings before they quietly wreck a batch.

Build a controlled deliverability test you can repeat

The test only means something if the sending side is external. A message sent from your own domain to your own catch-all can route internally and skip the MX path entirely, which hides exactly the problems you are looking for. Use a free mailbox on Gmail, Outlook, or any unrelated provider as the sender. For the recipient, pick a local part you have never used, something like probe-9f3k2x@yourdomain.tld. If the catch-all is configured correctly, that address does not need to exist in advance, because a catch-all inbox receives emails sent to any address on the domain.

Send a short plain-text message with a unique subject line and a timestamp in the body. Note the send time. Wait two to three minutes, then connect over POP3 or IMAP and look for the message. A catch-all domain service should deliver within seconds of the SMTP handshake completing, so a message that has not appeared in five minutes is a signal, not a coincidence. Check the spam or junk folder through IMAP as well, since some catch-all setups route to a default mailbox that filters aggressively.

When the message does not arrive, work backward through the chain. Query the domain’s MX records first. Then open a direct SMTP session to the MX host on port 25 and watch the response codes. A 250 after DATA means the server accepted it and the problem is downstream, in storage or retrieval. A 4xx or 5xx at RCPT TO means the recipient side is rejecting, which on a catch-all usually points to a misconfigured wildcard or a policy block. Keep a log of each probe with send time, MX host, response code, and retrieval time so you can spot trends instead of reacting to single failures.

Check the MX IP against DNSBLs after every batch

Deliverability testing tells you whether mail arrives now. DNSBL monitoring tells you whether it will keep arriving. Blacklists are the silent killer for anyone running SEO email accounts at volume: a listing can appear between batches, and while it is active, verification emails from some providers get rejected at the gateway before your catch-all ever sees them. The result looks like a broken catch-all when the real cause is a listed sending or receiving IP.

Look up the IP address of your MX host, not your website’s A record. They are often different machines. Check it against the major lists: Spamhaus ZEN, Barracuda, SpamCop, SORBS, and UCEPROTECT at minimum. POP3 catch-all mailbox has more details on this topic. Most providers publish a lookup form, and many DNSBLs answer directly over DNS so you can script the check. A simple dig against a reversed-IP zone returns either a listing code or NXDOMAIN. Run the check after every campaign batch and log the result next to your probe data.

One listing does not always mean blocked mail. Some lists are aggressive and some receiving providers ignore them. The practical question is whether your verification traffic actually drops, and the controlled test from the previous section answers it. Pair the two: if a DNSBL check returns a hit and your random-local-part probe also fails, you have a confirmed problem. If the probe still succeeds, the listing is low-impact but worth clearing before it spreads to more lists.

• Query MX records to find the actual receiving host, then check that IP rather than the domain’s A record.
• Check Spamhaus ZEN, Barracuda, SpamCop, SORBS, and UCEPROTECT after each batch.
• Log the listing status with a timestamp so you can see when a listing first appeared.
• Re-run the random-local-part probe immediately after any positive DNSBL result.
• Request delisting only after you have identified and fixed the cause, or it will return.

Keep the routine tight and the infrastructure clean

The routine is only as good as the domain underneath it. A catch-all email domain shared across too many tools and campaigns attracts complaints, and complaints drive listings. Keep separate domains for separate purposes, warm new domains gradually, and never point a fresh domain at a high-volume GSA SER or Xrumer run on day one. Tools like AllMail support GSA SER, RankerX, and Xrumer directly, and the platform monitors DNSBL blacklists so listing alerts arrive without you polling manually. It also offers POP3 and IMAP access, which is what lets you automate the retrieval half of the probe with a script instead of checking by hand.

Payment and identity handling matter more than most people admit. AllMail accepts crypto payments in USDT and USDC across TRC-20, BEP-20, and Polygon, requires zero KYC, and offers a 3-day free trial, so you can run the full test loop before committing. If you need an anonymous catch-all email setup for link building and scraper inboxes, that combination removes the identity trail that ties domains together. Set up the domain at allmail.one, point your probe script at the POP3 catch-all mailbox, and build the habit from day one.

Run the loop on this schedule: probe after setup, probe after every batch, DNSBL check after every batch, and a full review weekly. Keep the log in a simple spreadsheet with columns for date, probe address, MX host, SMTP response, retrieval time, and DNSBL status. When something breaks, the log tells you whether it was a one-off or the start of a pattern, and you fix it before the next batch goes out. That is the whole discipline: a random local part, an external sender, a POP3 confirmation, and a blacklist check, repeated often enough that nothing fails silently.