Can I scan both Cached and Online Exchange Stores simultaneously?

Scanning both locations simultaneously has both benefits and risks.

Technically, the answer is yes, but it is important to understand how the Spirion agent handles this process. When you set "Search only Cached Exchange Stores" to No, the Agent does not perform two separate, simultaneous scans; instead, it performs a unified, sequential scan that covers both locations.

Here is how the Agent handles this "simultaneous" search:

1. The "Hybrid" Scanning Logic

When the setting is set to No, the Agent follows this workflow:

Step 1 (Local): The Agent first scans everything available in the local .ost (cache) file. This is the fastest part of the scan.
Step 2 (Online): As the Agent crawls the mailbox hierarchy, it identifies folders or items that are not in the local cache (e.g., older emails or "Online Only" folders).
Step 3 (Fetch): The Agent then forces Outlook to request that specific data from the Exchange server. It "streams" the data down, scans it in memory, and then moves to the next item.

2. The "Online Archive" Exception

If you are trying to scan both a user's Primary Mailbox and their Online Archive at the same time:

You must set "Include Online Archive" to Yes.
You must set "Search only Cached Exchange Stores" to No.
Result: The agent will scan the local cache for the primary mailbox and then reach out to the server to scan the Online Archive (which is almost never cached).

3. Risks of Scanning Both (Setting to "No")

While this ensures the most complete scan possible, it introduces several risks that you should consider:

Performance Drag: The scan takes significantly longer. The "Online" portion of the scan is limited by your network speed and the Exchange server's responsiveness.
Outlook "Freezing": Because the Agent is forcing Outlook to download data, the user may see "Outlook is retrieving data from the server" messages or experience "Not Responding" hangs while the scan is active.
Network Throttling: If you are using Office 365, Microsoft may "throttle" the connection if the Agent requests too much data too quickly, which can cause the scan to fail or slow to a crawl.

4. When should you do this?

Do it when: You are performing a high-priority audit (e.g., a legal discovery or a security incident investigation) where missing a single old email is not an option.
Don't do it when: You are running a routine monthly scan for thousands of employees. In that scenario, it is better to set it to Yes (Cache Only) to protect network and server stability.

Tip: The "Slider" Factor

Remember that Outlook has a "Sync Slider" (e.g., "Keep mail for the last 1 year").

If you set Spirion to "Search only Cached Exchange Stores: Yes", it will only see that 1 year of mail.
If you need to see the mail from 2 years ago that is still on the server, you must set the option to No.

Summary

You can scan both by setting "Search only Cached Exchange Stores" to No. This tells the agent to start with the local cache and then automatically reach out to the Exchange server for any data that isn't stored locally.