Hi @Sandesh Budhathoki - DriveAway ,
Manual archiving is a client-side feature that allows the user to choose which messages or conversations to send to the server for archiving.
If you set the cached mode to 3 months, you will not be able to access the emails older than 3 months offline. They will reside only in your mailbox on the server and will not be available in your .ost file on your computer.
if you want to archive emails older than 3 months and also access them offline, you should either increase the cached mode setting or use the server-side archiving feature in Exchange. The server-side archiving feature moves emails from your primary mailbox to an archive mailbox on the server based on the retention policies applied to the messages by your administrator or yourself. You can learn more about In-Place Archiving in Exchange Server from this article.
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