Microsoft Outlook - Sent Emails Only Populate for the Last Month

Because the problem occurs in Classic Outlook, New Outlook, and OWA, it is not a local cache or “Download email for the past” issue; it indicates that only about one month of Sent Items actually exists in the mailbox on the server.

From the available information, the only supported client-side limitation that can hide older items is the Cached Exchange Mode “Mail to keep offline” / “Download email for the past” slider. This setting can cause only a subset of mailbox items (including Sent Items) to be synchronized to the local .ost file. When set to a limited period (for example, 1 or 3 months), items older than that period reside only on the server and are not available offline. However, this does not affect what is visible in OWA, which always shows the full server-side contents.

Given that OWA also only shows one month of Sent Items, the older sent messages are either:

• Deleted (and possibly still in Deleted Items/Recoverable Items), or
• Never created on the server (for example, sent from another account or client that stored sent mail elsewhere), or
• Removed by a server-side retention or cleanup process.

Client-side steps that can be verified from the provided material:

1. Confirm the offline sync window is not the cause
   • In Classic Outlook: File → Account Settings → Account Settings → Email tab → select the account → Change.
   • Ensure Mail to keep offline / Download email for the past is set to All. This guarantees that, if older Sent Items exist on the server, they will be cached locally.
2. Check whether “old” Sent Items are simply outside the sync window
   • If the slider was previously set to a limited period (for example, 12 months), older items would exist only on the server and not in the .ost. After changing the slider to All, restart Outlook and allow a full resync so that all available Sent Items are downloaded and indexed.
3. If older Sent Items still do not appear in Outlook or OWA
   • Because OWA is not affected by the sync slider, the absence of older Sent Items in OWA means they are not present in the mailbox.
   • At that point, recovery must be done on the service side (for example, from Deleted Items, Recoverable Items, backup, or archive), not via client cache settings.

Summary: The only client-side setting in scope here is the Cached Exchange Mode “Mail to keep offline” / “Download email for the past” slider, which must be set to All and allowed to resync. If OWA also shows only one month of Sent Items after that, the older messages are no longer in the mailbox and must be recovered using server-side tools or backups rather than Outlook client configuration.

References:

• Only a subset of your Exchange mailbox items are synchronized in Outlook
• Troubleshooting Outlook search issues
• View sent email