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An email you were expecting has not arrived. The first thing to establish is whether it reached our server at all, because that splits the problem in two and everything else follows from it.
Start with Track Delivery. In cPanel, open Track Delivery in the Email section, enter the sender’s address and run the report.
  • The message appears — it reached us. The problem is on this side: a filter, a full mailbox, or the wrong folder. Work through the checks below
  • Nothing appears — it never reached us. Skip to when the message never arrived

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Check these five things first

In rough order of how often they turn out to be the cause.

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1. Your mailbox is full

A mailbox at 100% of its quota rejects incoming mail. Nothing arrives and nothing is held for you. Check the mailbox’s usage in your control panel, and clear space if it is at its limit. Senders see a 552 5.2.2 bounce, which means exactly this: the recipient address is over quota.
If mail still does not arrive shortly after you free up space, the mailbox may need a backend reset at our end. Open a ticket and say you have cleared the quota.

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2. It went to Junk, Spam or Trash

Log in to webmail rather than checking in your mail app, so you are looking at what is actually on the server. Check Junk, Spam and Trash — legitimate messages do get caught, and filters sometimes delete rather than divert. On Professional Email, add the sender to your trusted senders list: Settings (gear icon) → Antispam or Content Filtering → add the address or domain. Worth doing for transactional and one-time-code emails, which are the ones most often filtered.

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3. A filter is discarding it

Check Email Filters in your control panel for any rule that discards, forwards or redirects incoming mail. Rules set up long ago and forgotten are a common cause, particularly ones created by a previous administrator.

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4. The mailbox does not actually exist

If mail to one address bounces while others work, check the mailbox has been created. A message to an address with no mailbox bounces with 554 5.0.0. This catches people out after a migration, where the DNS is right but the mailboxes were never recreated.
Using a catch-all? The mail gateway may check whether the specific address exists before the catch-all rule applies, and reject the message with Relay access denied if it does not. If particular addresses need to work reliably, create an explicit forwarder or alias for each rather than relying on the catch-all.

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5. Your MX records point somewhere else

If you have recently changed nameservers or moved hosting, check the MX records in your DNS zone actually point here — mail.example.com or your server — rather than at a previous mail host or spam-filtering provider. Also check Email Routing in your control panel is set to Local Mail Exchanger, so the server treats mail for your domain as belonging to local mailboxes. See MX records and mail routing, which covers the mail A record and the Local/Remote setting in detail.

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Confirm the mailbox can receive at all

Send a test message from an outside account — Gmail or Outlook — to the address.
Do not put “test” in the subject or body. Messages containing test, placeholder text or random strings are very likely to be filtered as spam, and you will diagnose a problem you do not have. Write something ordinary instead.
If one mailbox on the domain is failing while forwarders or other mailboxes work, the problem is that mailbox — quota or filters — not your domain’s DNS.

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When the message never arrived

If Track Delivery shows nothing, the message did not reach us. That means either the sender’s server never delivered it, or it was rejected at our gateway before it was accepted. Raise a ticket and include:
  • The sender’s email address
  • The exact recipient address
  • The approximate date and time
We can then trace the mail server logs for that transaction and tell you whether it was rejected, and why. Without those three details the logs cannot be searched usefully, which is the main reason these conversations go back and forth.
Bounced or rejected mail cannot be recovered. A message that never reached the server is not in any backup and is not sitting in a queue. The only option is for the sender to send it again.The same applies to mail misrouted to an old host after a DNS change — it bounces to the sender immediately rather than waiting for you.

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Errors you might see in a bounce

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Still nothing?

A few less common causes worth mentioning on a ticket:
  • Strict senders needing TLS. Some services, Amazon SES among them, will refuse to deliver without STARTTLS on our inbound gateway. Ask us to confirm it is enabled for your domain rather than relying on a third-party checker, as those often report inaccurately
  • Connections dropping mid-session, where mail starts to deliver and then stops. We can see from the logs which SMTP command it failed at
  • One sender failing while everyone else works. Usually their end, but the logs will show whether we rejected it
If you cannot stay in a live chat long enough to work through this, ask the agent to open a ticket for you. The technical team can then investigate and reply to your registered address.