To migrate user alerts, the Server Extension needs to be installed on your on-premises source and on-premises destination server(s). For more information see, List of values the Server Extension preserves.
For installation instructions, see the article Installation - Server Extension.
To prevent user alerts from being triggered during a copy to an on-premises environment, you must be farm admin at the destination.
The Server Extension is only required for on-premises environments and is not required in your Microsoft 365 environment.
When copying to a Microsoft 365 environment, there is no way to prevent user alerts from being triggered. Since it is a migration to a cloud environment, the ShareGate migration tool does not have the information on when certain tasks are completed, which may result in alerts being triggered during the copy.
The Server Extension is not compatible with SharePoint 2003. Therefore, the migration of user alerts from a SharePoint 2003 server is not supported.
Note: As of November 2021, the ShareGate migration tool is no longer able to provide full support for SharePoint Server 2003 and 2007, which are past the end of their Microsoft support lifetime. For more information, see Contacting our technical support team.