Email problems, diagnosed in plain English.
Enter your domain for a full checkup: where your mail lives, who runs each piece, what's healthy, and what to fix first. Answer a few questions and the diagnosis gets more specific. Got a bounced email? Paste the error and get it decoded.
Who is affected?
What's broken?
When did it start?
Anything change recently? (pick any)
Headers include the subject line and the addresses involved. Nothing pasted here is stored after your session, and the diagnosis works fine if you delete the subject line first.
Free checkup, fair-use limits apply. Planning a move between platforms? The Migration Mapper runs on this same engine.
Twenty-five of them, grouped by what is broken, plus the free and paid tools worth using, live in the email toolbox.
| Symptom | Usual cause | First move |
|---|---|---|
| Mail lands in spam at Gmail and Yahoo | Missing SPF, DKIM, or DMARC. Both providers now require authentication from senders, and bulk senders get held to a one-line DMARC minimum. | Run the checkup above; fix SPF and DKIM first, then add DMARC p=none. |
| Bounces that mention 550 5.7.x or 'unauthenticated' | Same authentication gap, seen from the receiving side. | Paste the bounce above; the decoder assigns the fix. |
| Mail suddenly stopped for everyone | DNS change, expired domain, or provider outage. The date rows above often solve this one alone. | Check the outage link and the key dates in Who Runs What. |
| One person stopped receiving | A forwarding rule, a full mailbox, or quarantine holding their mail. | Admin console checklist above: rules, quota, quarantine, in that order. |
| New marketing or CRM tool's emails bounce or spam-fold | The tool was never added to SPF and never given a DKIM key. | Add the tool's include to SPF and turn on its DKIM in the tool's settings. |
| Can't sign in, or Outlook keeps asking for a password | The work-or-school vs personal Microsoft account mix-up, or an expired session after a security change. | Sign fully out everywhere, sign back in with the correct account type. |
| Outlook shows old mail or won't send, web mail works fine | Client-side: Work Offline mode, a stale cache, or a broken profile. | Check Work Offline, then restart in safe mode (outlook.exe /safe), then rebuild the profile. |
| Large attachment won't send | Message size limits, typically around 25 MB at most providers. | Share a link instead (OneDrive, Google Drive), or raise the limit if you control it. |
| Phone stopped syncing but the computer is fine | Account needs re-authentication on the device, or the OS is throttling the mail app. | Remove and re-add the account on the device; check battery and sync settings on Android. |
| Emails to one specific company always fail | Their security filter dislikes something about your setup, or an old server of yours is on a blocklist. | Send the exact bounce text through the decoder above; it names whose side the problem is on. |
Microsoft (free)
- Support and Recovery Assistant (SaRA) : automated fixer for Outlook and account problems on Windows
- Remote Connectivity Analyzer : tests Microsoft 365 mail flow, autodiscover, and inbound SMTP from outside
- Message Header Analyzer : paste raw email headers, see the delivery path and auth results decoded
Google (free)
- Admin Toolbox : Dig, CheckMX, and a header analyzer from Google's own support team
- Postmaster Tools : how Gmail sees your domain's reputation and authentication, if you send volume
- Email Log Search : in the Workspace Admin console: trace exactly what happened to any message
Apple (built in)
- Mail Connection Doctor : Apple Mail, Window menu: live per-account connection testing
General (free)
- mail-tester.com : send it one email, get a deliverability score with the reasons
- MXToolbox : the classic record-lookup swiss army knife, if you can read the output
- DMARC record checker (dmarcian) : sanity-check your DMARC record's syntax and policy
Lookups run fresh against public DNS and registry data. Your answers and any bounce text are processed to build the diagnosis and are not stored after your session. The linked tools above are third-party services with no affiliation; they were picked because they work.
This checkup is diagnostic guidance built from public records and your answers, not a guarantee. Before editing DNS: change one record at a time, write down what it said before, and give changes up to an hour to take effect before judging the result. Changes you make to your own systems are your responsibility: this tool reads public records and cannot see or safeguard your environment. When mail is business-critical and the fix is unclear, have a professional look before you change anything.