Policy
Interval between new Outlook migration attempts
This policy setting controls the interval between new Outlook migration attempts. If you don't set this or set this to 0 (default value), classic Outlook will stop executing "New Outlook auto migration" after the user toggles back to classic Outlook for Windows. If you set this to 1, classic Outlook will show a blocking prompt on each app launch, which will attempt to switch the user to the new Outlook app. If you set this to N (2 - 9900) value, "New Outlook auto migration" will be re-initiated N days after the user toggles back to classic Outlook. Note: This policy only applies to subscription-based Microsoft 365 Apps.
d6192ff44fba L_NewOutlookAutoMigrationRetryIntervals Registry
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HKCU\software\policies\microsoft\office\16.0\outlook\options\general\newoutlookautomigrationretryintervalsPolicy notes
This policy setting controls the interval between new Outlook migration attempts. If you don't set this or set this to 0 (default value), classic Outlook will stop executing "New Outlook auto migration" after the user toggles back to classic Outlook for Windows. If you set this to 1, classic Outlook will show a blocking prompt on each app launch, which will attempt to switch the user to the new Outlook app. If you set this to N (2 - 9900) value, "New Outlook auto migration" will be re-initiated N days after the user toggles back to classic Outlook. Note: This policy only applies to subscription-based Microsoft 365 Apps.