Start with the account you can access now and make a few safe comparisons. An email app is only the viewing and sending tool. The email provider stores the mailbox. For example, Outlook can be the app used to access a Gmail account. That distinction helps you test the right place without making a destructive change.
Start here
Start with the least disruptive checks
Use these checks in order. Stop when you find a clear difference, and keep sign-in recovery as a separate problem.
Compare mailbox and appOpen the provider's webmail in the current browser, then compare it with the app on the same account.Read this part
Locate missing mailCheck the account, folders and visible filters before assuming a message has disappeared.Read this part
Test deliveryUse a small, voluntary send-and-reply test with a trusted contact or another account you control.Read this part
Check the connection and the mailbox
First confirm that the device can open a few ordinary websites. If everything is slow or offline, email may only be showing the wider connection problem. If other websites work, open your provider's webmail in the browser. Use the provider's normal sign-in page and the account you intend to check.
If new messages appear in webmail but not in the app, the mailbox may be working while the app is not updating. If neither webmail nor the app shows new mail, the issue may be with the provider, account access, storage or the sender's delivery attempt. A message that has not reached the provider cannot be recovered from the app.
For a wider connection fault, see Wi-Fi dropouts diagnosis.
Understand the app and provider
The app on your phone or computer is not necessarily the company that provides your email. Outlook may be the app while Gmail is the provider. Apple Mail may display an account hosted elsewhere. This is why webmail is a useful comparison: it checks the mailbox without relying on the app's local display or sync state.
On Android Gmail, pulling down can request a refresh. Google also recommends checking that the app is current, restarting the device, and checking Menu → Settings → your account → Data usage → Sync Gmail. Sync is not always instant. The device's available storage is also different from the shared storage quota for the Google account. See the Gmail troubleshooting guidance.
On current iPhone and iPad software, Settings → Apps → Mail → Mail Accounts → Fetch New Data controls when mail is checked. Settings → Notifications → Mail controls alerts. They do not prove that a message reached the provider. Apple also warns that a backup preserves mail settings rather than the email itself. See Apple's Mail troubleshooting guidance.
Check storage, status and access separately
Look for a clear storage warning in webmail or the provider's account page. A full provider mailbox can prevent sending or receiving. For Outlook.com, messages sent while the mailbox is full may bounce and do not automatically reappear after space is later available. This applies to the Outlook.com service, not to every account viewed in the Outlook app. See Microsoft's Outlook.com guidance.
Also check the provider's status page if the mailbox itself is unavailable. Do not treat a sign-in problem as a sync problem. If you cannot access the account, use the provider's official recovery route rather than repeatedly changing app settings.
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If you’d rather have local help, see our personal email troubleshooting help.