When business email stops arriving, the mailbox platform is only one part of the delivery path. DNS, MX records, authentication, filtering, forwarding, storage limits and desktop clients can all produce similar complaints. The exact symptom is the fastest guide to the cause.
Define the exact email symptom
Determine whether all external mail is missing, only one sender is affected, outgoing mail fails, messages arrive in spam, or the web mailbox works while Outlook does not. These are different problems.
If a sender receives a bounce message, keep the complete message and diagnostic code. It often identifies the rejecting server, policy or unavailable mailbox. Without that evidence, teams can spend time changing unrelated DNS records.
Check MX records for inbound delivery
MX records tell other mail systems where to deliver messages for your domain. Missing records, records for an old provider, incorrect priorities or a partially completed migration can send mail to the wrong place.
Compare the public MX records with the exact values required by the active email provider. If the company recently moved between Microsoft 365, Google Workspace or another provider, confirm that old routes and connectors are no longer handling part of the traffic.
Understand SPF, DKIM and DMARC
SPF lists systems authorized to send mail for the domain. DKIM adds a cryptographic signature that receiving servers can verify. DMARC tells receivers how to evaluate alignment and where to send reports.
These records mainly affect trust in outgoing mail, but incorrect configurations can cause messages to be rejected or placed in spam. Avoid creating several independent SPF records at the root domain; combine authorized senders according to the provider's documented configuration. Introduce strict DMARC enforcement only after legitimate mail sources have been identified.
Mailbox limits, forwarding and filtering
A full or disabled mailbox may reject new messages. Forwarding rules, shared-mailbox permissions, transport rules, quarantine policies and user-created inbox rules can make messages appear to disappear.
Check the web interface first. Review storage usage, account status, quarantine, spam folders and recent rules. If only one sender or domain is affected, review allow/block lists and message-trace information instead of changing the entire mail system.
Desktop and mobile client configuration
If mail appears in the web mailbox but not in Outlook, Apple Mail or a phone, the delivery system is working. Focus on account authentication, sync status, cached profiles, IMAP settings, application passwords and local filters.
Do not repeatedly change DNS when the message is already present on the server. Test with the provider's web interface to separate server-side delivery from local synchronization.
Collect evidence before making changes
- Sender and recipient addresses.
- Approximate sending time and message subject.
- Complete bounce message or delivery-status notification.
- Whether the message appears in webmail, quarantine or spam.
- Current email provider and any recent migration.
- Public MX, SPF, DKIM and DMARC records.
DNS changes can affect websites, verification records and other services. Export or document the current zone before removing records, and change only entries connected to the confirmed problem.
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