Missing Email post-migration
From Exchange or Office 365 to anywhere.
(1) Supported Item Classes
This is the most common reason for "missing" email from Exchange/365. CloudMigrator, by default, will migrate only IPM.Note and IPM.Note* subclasses (these are true emails). Anything outside of these classes will be skipped (not failed) and, therefore, not reported against. Item classes outside of IPM.Note are typically NDRs or other reports that are, generally, unwanted items. If you wish to include other classes, you can do so via Source Platform > Advanced Settings > Message Options > Included Item Classes, however, please note that other classes are unsupported as there may be conversion issues that we cannot resolve. See here for more information from Microsoft.
(2) Emails which exist in multiple folders
Copies of emails which exist in multiple folders will only be migrated once, from the first folder in which they are found. For all other folders, they will be skipped as "Already Exists". This may result in whole folders contents not being migrated. There is no solution that CloudMigrator can provide for this issue.
(3) Litigation Hold
Are the missing emails in "litigation hold"/"recoverable items? These emails will not be visible in the migration reports (as failures), however, CloudMigrator has a new setting 'Include Recoverable Mail Items' in the source Exchange platform settings which can be enabled to allow the migration of these emails.
You can use Powershell to find out if this is enabled for a user:
get-mailbox username |ft litigation*
(4) Exchange Online Archive
If you want to migrate data that is stored in Exchange Online Archive, this is stored separately, and therefore migrated separately. See this article.
(5) Retention Policy
If there is a retention policy enabled on the destination Exchange/365 then the mail may be migrated and archived immediately and, therefore, appear to be missing in the destination but just be archived.
(6) Other Third Party Archiving
We recommend disabling any third party archiving solutions to avoid any issues.
(7) Possible changes
There may also be Possible Changes to Migrated Items