Outbound success does not test inbound delivery
Send a controlled external message and locate where it stops: DNS routing, server delivery, filtering or client retrieval.
Sending success says little about incoming MX, mailbox delivery or client synchronisation. For a previously working entitled mailbox, follow one controlled external message until it stops. Keep MX and mailbox state unchanged until the failure point is known.
Confirm the exact address and ask a sender outside the domain to send a uniquely labelled, non-sensitive message. Record send time and any delivery-status notification; do not use a form or application on the same host as the only test.
Separate the mailbox from its client
Check the provider-supported webmail view, if available, before changing the desktop or phone application. If the message appears in webmail but not the client, inspect folder selection, IMAP or POP configuration, synchronisation errors and local filters. Search Spam and other server-side folders. Mozilla’s receiving guide recommends checking account and server settings. If POP is used on more than one device, one client may have downloaded and removed a message from the server depending on settings.
If the controlled message appears in provider webmail but not the phone, the server received it; inspect the phone's folder and sync settings before touching MX.
If webmail also lacks the test message, check whether the sender received a bounce. A “user unknown” response points towards recipient address or mailbox state; a temporary deferral or quota error needs the provider’s delivery trace. Absence of a bounce is not proof of delivery.
Trace MX and server delivery
Query the domain’s public MX answers at the authoritative DNS provider and resolve each MX target. Compare the answers with the mail operator’s intended route, including any transition still inside prior TTLs. If no MX exists, SMTP may try the domain’s address as an implicit fallback, which could point at a website instead. Check whether the domain registration or DNS authority changed. Do not replace valid records based only on one resolver’s cached answer.
If routing appears right, ask the mail operator to trace the unique message by recipient, sender, timestamp and message ID. The trace can distinguish no connection, acceptance and delivery to the mailbox, quarantine, or rejection. Spam filtering and mailbox quota/state should be checked in the actual provider system, not assumed from the client display.
Repair one proven cause and verify receipt
Correct a client setting only when webmail proved server delivery. Correct a DNS route only when authoritative answers differ from the intended mail provider, with a saved rollback record and a controlled overlap plan. If the server accepted but quarantined the message, use its supported review process rather than disabling filtering globally. After repair, request a fresh message from the same external sender and verify its arrival in both webmail and the intended client.
Escalate with redacted addresses, the unique subject token, timestamps, bounce text and MX answers. Do not send mailbox passwords. Keep the old mail route available during an authorised migration until new inbound tests pass.
Common questions
Why can I send but not receive? Submission and inbound delivery are independent paths.
Should I delete and recreate the mailbox? No; that risks data loss without locating the fault.
Can Spam hide a message? Yes; check server-side filtering and quarantine before editing DNS.
Does a correct MX answer prove mailbox delivery? No. The mail operator must confirm acceptance, filtering and mailbox placement.
Sources and technical references
Related guides
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