By David, , updated
Yes, use Outlook in Cached Exchange Mode on Azure Virtual Desktop (AVD), and keep the cache in the user's FSLogix container with a short sync window. Microsoft's own AVD image guidance turns Cached Exchange Mode on and limits it to one month of mail and one month of calendar, which keeps the OST small enough to roam in a profile container without slowing sign-in.
The short version: set Cached Exchange Mode on, with a one-month mail and calendar sync window, by policy. Store the OST in the FSLogix profile container (or an Office container) so it survives sign-out on pooled hosts. Size containers for the OST plus OneDrive, and keep Windows Search running if users rely on fast Outlook search.
Why cached mode matters on pooled hosts
In Cached Exchange Mode, Outlook keeps a local copy of the mailbox in an OST file and works from it. In Online Mode, every folder click goes to Exchange Online. On a single PC, cached mode is the default for a reason: Outlook is faster and more tolerant of network blips.
On a pooled AVD host there's a catch. The user lands on a different host each day, and anything written to the local disk is gone at sign-out. An OST that isn't roamed has to be rebuilt from scratch every session, which is the worst of both worlds: Outlook downloads mail constantly and the user waits.
FSLogix fixes that. With a profile container, the OST lives inside the user's VHDX on the file share and comes back with them on any host. Microsoft recommends one container for the whole profile, Office data included, and the default ODFC (Office) container includes Outlook data when you choose to split it out (FSLogix container types).
| Option | How it behaves on pooled AVD | When to use it |
|---|---|---|
| Cached mode, OST in the profile container | Fast Outlook, OST roams with the user | The default for most deployments |
| Cached mode, OST in a separate ODFC container | Same, with Office data on its own disk and size limit | Large mailboxes, or a profile solution other than FSLogix |
| Cached mode, OST not roamed | OST rebuilt every session, heavy network and slow start | Avoid |
| Online mode | No OST, every action goes to the server | Very small or kiosk-style use, or users with a tiny mailbox |
Recommended Outlook settings for AVD
Microsoft's AVD image guidance sets these per-user policy values in the default user hive (Install Office on a custom VHD image), under software\policies\microsoft\office\16.0\outlook\cached mode:
| Value | Data | Effect |
|---|---|---|
enable | 1 | Turns on Cached Exchange Mode |
syncwindowsetting | 1 | Keeps one month of mail in the OST |
CalendarSyncWindowSetting | 1 | Limits the cached calendar |
CalendarSyncWindowSettingMonths | 1 | Sets that calendar window to one month |
Mail older than the sync window is still there: Outlook fetches it from the server when the user scrolls or searches past the window. Set the same values through Group Policy or Intune with the Office administrative templates if you'd rather not touch the default user hive.
The same guidance installs Microsoft 365 Apps with shared computer activation, which multi-session hosts need, and with automatic updates off, so Office is updated with the image.
Sizing the profile container for Outlook
The OST is usually the biggest single thing in a profile container. A one-month window keeps it predictable, but plan for:
- The OST itself, which grows with mail volume, attachments and shared mailboxes added in cached mode.
- OneDrive's local cache, if you also roam OneDrive in the same container. See OneDrive on AVD multi-session.
- Teams and browser caches, which add up across a working week.
Microsoft's FSLogix guidance gives an example of splitting containers to give Office data more room, such as a 10 GB profile container with a 50 GB ODFC container. Whichever layout you choose, watch the file share's free space: a full share turns into temporary profiles for everyone on it. FSLogix troubleshooting covers what that looks like.
Outlook search on AVD
Outlook's instant search in cached mode uses the Windows Search index on the session host. If the Windows Search service is disabled, Outlook search is slower and less complete, and users notice it first in large mailboxes.
Many optimization baselines turn Windows Search indexing off to save disk IO. That's a reasonable default for a general pool, but not for a pool of heavy Outlook users.
Troubleshooting Outlook on AVD
| Symptom | Likely cause | Fix |
|---|---|---|
| Outlook downloads all mail every morning | OST isn't being roamed | Check the FSLogix container attaches, and that the OST path isn't excluded |
| "Your profile couldn't be loaded" after weeks of use | Container or share is full | Raise the container size limit or free share space |
| Outlook slow to open | Large OST, or Online Mode by mistake | Confirm cached mode is on with a one-month window |
| Search is slow or returns partial results | Windows Search disabled on the hosts | Turn indexing back on for this pool |
| Activation errors | Shared computer activation not enabled | Reinstall or set SharedComputerLicensing |
| Shared mailboxes make Outlook slow | Shared mailboxes cached into the OST | Consider not caching shared folders for heavy users |
On pooled AVD hosts, cached mode only works if the OST roams. Put it in the FSLogix container, keep the sync window short, and watch the share's free space.
Where Atlas AVD helps
- FSLogix capacity, watched for you. FSLogix Management lists each pool's profile containers with their size and last use, and checks file share capacity every 15 minutes, warning at 85%. When an OST pushes a container toward its limit, you see it before the user's next sign-in fails.
- Profile actions without RDP. Reset Profile, Detach Container and Mark for Rebuild fix a broken container from the console.
- Search indexing per pool. Atlas's Windows Desktop Optimization includes a Search Index Optimization module, on by default, which disables Windows Search indexing. For a pool of heavy Outlook users, override that one module on the pool and leave the rest of the optimization on. The WDOT post explains the modules and per-pool overrides.
That's the real Atlas AVD console in our demo environment; the pools and shares are sample data. Atlas doesn't set Outlook's cached mode policies: use Group Policy, Intune or your image for those.
FAQ
Should Outlook use cached mode on Azure Virtual Desktop?
Yes, for most users, as long as the OST is stored in an FSLogix profile or Office container so it roams between hosts. Microsoft's AVD image guidance enables Cached Exchange Mode with a one-month sync window.
Where should the Outlook OST live on AVD?
Inside the user's FSLogix profile container, or in an ODFC (Office) container if you split Office data out. Never only on the session host's local disk on a pooled pool.
What sync window should I use for Outlook on AVD?
Microsoft's AVD image guidance uses one month for mail and one month for calendar. Older items are still available from the server on demand.
Do I need an ODFC container for Outlook?
No. FSLogix recommends a single profile container holding profile and Office data together. A separate ODFC container is optional, and useful when you want different size limits or another profile solution handles the rest of the profile.
Why is Outlook search slow on AVD?
Usually because Windows Search indexing is turned off on the session hosts, which many optimization baselines do to save disk IO. Turn it back on for pools of heavy Outlook users.
Does the slow logon problem relate to Outlook?
It can. A large OST makes the container bigger and a full share causes failed sign-ins. See why AVD logons are slow for the full checklist.
Last updated 9 November 2026. Microsoft details are drawn from Microsoft Learn as of November 2026: Install Office on a custom VHD image and FSLogix types of containers. Check them before you change production settings.