Email delivery troubleshooting: Fix missing emails

A missing email does not always mean your inbox is broken. The message may be delayed, filtered, rejected, or sent to the wrong address — and these fail in ways that look identical from the mailbox.

This is an ordered procedure for narrowing it down. Work through it in sequence; the early steps eliminate the most common causes cheaply. For an explanation of why each failure happens rather than what to do about it, see why you're not receiving emails.

How to troubleshoot a missing email

1. Establish a known-good baseline

Before changing anything, find out whether the mailbox receives mail at all from an independent sender. This separates "this mailbox is broken" from "this one message went missing," which are different investigations.

Send a controlled message from outside your own domain and provider — sending between two accounts at the same provider can be delivered internally and prove nothing about external mail. A test message works, as does asking someone on an unrelated provider.

Check the address carefully while you are there:

Then note the SMTP-level result — accepted, rejected, or deferred — separately from whether anything appeared. The delivery status shows this. A rejection points at routing or the address; acceptance with nothing visible points at filtering.

2. Check the whole mailbox

Do not look only in the main inbox.

Search:

In Gmail, in:anywhere covers Spam and Trash, which an ordinary search excludes. On a business account, the organisational quarantine is invisible to the user — an administrator has to check it, and it is a frequent hiding place.

If you find the message in Spam, mark it as Not spam. That confirms the mailbox received it and the problem is placement, not delivery. See how to check if incoming emails go to spam for what changes the outcome.

3. Check webmail

Open the mailbox directly in Gmail, Outlook on the web, iCloud Mail, or your provider's website.

If the message appears there but not in your email app, the problem is synchronisation rather than delivery. Refresh the mailbox and allow a few minutes before testing again.

4. Review blocked senders and inbox rules

A rule may be moving, deleting, or forwarding the message automatically. Rules run after delivery, so a message can be accepted and disposed of within seconds.

Check for rules involving:

For business accounts, ask an administrator to check security policies and quarantine records.

5. Check mailbox storage

A full mailbox rejects new messages, usually with a 552 or 452 storage code.

Delete unnecessary emails and large attachments, then empty Trash and Junk. Note that on Google accounts, Drive and Gmail share one allocation — a full Drive stops mail. Send a new test after freeing space.

6. Try another sender

Send messages from more than one source:

The pattern identifies the cause:

7. Check for a bounce

When a receiving server rejects a message, the sender may receive a bounce notice. Ask them to forward it — that text is often the most useful evidence available.

Look for phrases such as:

A hard bounce (5xx) usually means a permanent problem, such as an invalid address. A temporary bounce (4xx) may be caused by a full mailbox, an unavailable server, greylisting, or a rate limit — sending servers retry these for a day or more before giving up.

8. Check forwarding and aliases

Messages may be redirected without appearing in the original inbox.

Confirm that:

Try sending directly to both the forwarding address and the final destination. Note that forwarding commonly breaks SPF validation, so forwarded mail is filtered more aggressively at the destination.

9. Check MX records for custom domains

For addresses using a custom domain, MX records tell senders where email should be delivered.

Check that:

Look them up with dig MX yourdomain.com +short or an online DNS lookup. Incorrect MX records can prevent email from reaching every mailbox on the domain. MX, DNS, and mail routing explained covers what the output should look like.

Do not change DNS records unless you control the domain and understand the current setup.

10. Check sender authentication

When messages from one sender repeatedly fail, the problem may involve SPF, DKIM, or DMARC.

These records help inbox providers verify that a sender is legitimate. Authentication failures can cause messages to be rejected or placed in Spam — and requirements tightened in 2024, so senders who were fine for years may have started failing.

Ask the sender or their administrator to check:

Google publishes current email sender guidelines for messages sent to Gmail accounts.

11. Use message tracing for business email

Microsoft 365 and other business platforms provide message tracing tools, and this is stronger evidence than any external test.

An administrator can check whether the message was:

Provide the sender, recipient, approximate time, subject, and any bounce code. Microsoft explains how to trace email messages. Google Workspace offers the equivalent through Email Log Search.

What each delivery result means

Sent

The sending service accepted the request and attempted delivery. This does not yet prove that the receiving server accepted the message.

Delivered

The receiving mail server accepted the email. It may still appear in Spam, quarantine, Promotions, or another folder — acceptance and placement are separate decisions.

Bounced

The receiving system rejected the message. Check the address, mailbox status, domain setup, and bounce details.

Pending

The receiving server may be delayed or temporarily unavailable. Wait a few minutes and refresh the delivery status.

Is my inbox working?

Your inbox is probably working when:

Your inbox may need attention when:

One missing email is not enough to diagnose the whole mailbox. Run a fresh test and compare results from more than one sender.

Frequently asked questions

Why didn't I get the test email?

The most common causes are a mistyped address, spam filtering, inbox rules, forwarding, a full mailbox, or a temporary delay. Check every mailbox folder and review the delivery status.

How can I test if my email works?

Send a message from an independent sender and check your inbox, Spam folder, and the SMTP-level result. How to test whether an email address can receive mail covers how to construct a test that actually proves something.

Can an email be delivered but not appear in my inbox?

Yes. Delivered means the receiving server accepted it. The provider may still place it in Spam, quarantine, or another folder.

Why can I receive some emails but not others?

The failing sender may have an authentication or reputation problem. Your mailbox may also contain a rule that affects only that sender.

How long should I wait before treating a message as lost?

Deferred mail retries for a day or more. Anything within a few hours is unremarkable. Permanent rejections are immediate.

Does a testing service read my inbox?

It should not, and sending a test message does not require it. Reading a mailbox needs credentials or an OAuth grant — a different level of access entirely. See what email testing tools can see.

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Still unsure whether your inbox is working? Send a free test email and check the delivery status.