Exchange Online and Outlook troubleshooting information

Migration Exchange Web Services (EWS) throttling policy

Verify that the EWS throttling policy isn't too restrictive for a mailbox data migration that uses third-party tools. (Doesn't apply to Microsoft tools for Hybrid, IMAP, G Suite, or Public Folder migrations.)

Run Tests: EWS Throttling

Mailbox or message size

Check the size of a mailbox or the size of messages (including attachments).

Run Tests: Mailbox Size

Increase or customize Exchange Online mailbox size

Deleted mailbox diagnostics

Check the state of recently deleted mailboxes.

Run Tests: Deleted Mailbox

Delete or restore user mailboxes in Exchange Online

Exchange Remote PowerShell throttling policy

Update the Exchange Remote PowerShell throttling policy for the tenant.

Run Tests: PowerShell Throttling

Email delivery troubleshooter

Check whether email messages are successfully delivered.

Run Tests: Email Delivery

Find and fix email delivery issues

Outlook user connectivity diagnostics

Diagnose Outlook connectivity issues for users by running several checks on possible service-side settings (root causes) so that a tenant admin can quickly fix the issues without involving the users.

Run Tests: Outlook User Connectivity

Fix Outlook connectivity issue

Non-delivery report (NDR) diagnostics

Provide additional information about NDRs that are received through email messages.

Run Tests: Email NDR

Email non-delivery reports in Exchange Online

Archive mailbox diagnostics

Check and identify issues about mailbox archiving.

Run Tests: Archive Mailbox

Enable archive mailboxes in the Microsoft 365 compliance center

Outlook user password prompt diagnostics

Diagnose Outlook password prompt issues for users by running several checks on possible service-side settings (root causes) so that a tenant admin can quickly fix the issues without involving the users.

Run Tests: Outlook Password Prompt

Fix Outlook password prompt issue

Retention policy diagnostics

Check retention policy settings.

Run Tests: Retention Policy

Retention tags and retention policies in Exchange Online

Enable Basic authentication in Exchange Online

Enable Basic authentication for legacy protocols in Exchange Online if previously disabled by Microsoft, or opt out of the disabling process if there is a need to use Basic authentication with specific legacy protocols.

Run Tests: Basic Auth in EXO

Basic Authentication and Exchange Online – June 2021 Update

DomainKeys Identified Mail (DKIM) diagnostics

Validate that DKIM signing is configured correctly and the correct DNS entries have been published.

Run Tests: DKIM

Use DKIM to validate outbound email sent from your custom domain