Posted: 9/6/2009, Updated: 8/2/2010
The short answer is, "Yes." Spirion will attempt to search OST files in almost all cases unless there are specific configuration issues or the OST is obsolete (i.e., corrupt, not attached to a profile or no longer associated with an exchange account). There are a lot of technical details behind this, available below, but the information is generally only of interest/useful if unexpected behaviors or search issues are being experienced.
Unfortunately Microsoft does not expose how OST files are managed or how e-mail data is synchronized between an Exchange server and Outlook via the OST file. We have performed extensive testing in a number of scenarios and worked with our customers to develop a comprehensive search capability. Please note that no Exchange e-mail (OST or server) will be searched if the "Search remote mail folders" option within the Spirion E-Mail Search settings is disabled (as it is by default).
Based on our experience:
- If Outlook is configured to "Use Cached Exchange Mode" then Spirion will attempt to search the OST file, but if the OST is out of date or unavailable it will attempt to search the Exchange Server. Spirion can only search the Exchange Server if Outlook is open and properly authenticated - or - if Outlook is closed and the Exchange server credentials are tied to the user account at an operating system level (i.e, credentials are cached). When Spirion cannot connect to the Exchange server, it will still search the OST file, but only locally cached copies of messages will be searched (any messages that have not been downloaded will be skipped). In this case the Exchange server is usually contacted once at the beginning of a search in Spirion, ostensibly to attempt to use cached/operating system credentials, but regardless of whether or not the authentication succeeds or fails, the contact is generally only a few kilobytes of data and subsequently the OST file is searched.
- If Outlook is open and the user has selected "Offline" mode, then only locally cached copies of messages (found in the OST files) are searched and the Exchange server is not contacted.
- If Outlook is open and the user is logged in, or the Exchange account credentials are cached and tied to the operating system user, then Spirion is able to obtain access to the Exchange server. In this case what we have experienced is that if a user has a message fully downloaded with attachments, then the cached copy (in the OST file) is searched and the entire message is not retrieved from the Exchange server. However, if any parts of the message are not downloaded (e.g., if the user is on a slow connection, or if replication is out of sync, or attachments were never fully downloaded) then the entire message will be downloaded from the Exchange server before it is searched. Unfortunately, even if Outlook has been told to always download full messages, it may not always do so because of a slow connection in the rare case that the Exchange server is unavailable or becomes unavailable during an email transfer as well as in other cases that are unknown (not documented by Microsoft). We have also seen that if an OST file has become corrupt or needs to otherwise be re-indexed that some or all of the messages in the OST may be downloaded in part or in their entirety from the Exchange server. This last case is rare, but it does occasionally happen, for example, if Outlook crashed or did not otherwise properly shut down.
- If Outlook is open, the user is logged in, and their Exchange account is configured not to cache any messages to the client, then Spirion may attempt to download the full message and attachments from the Exchange server each time a search or preview is performed. While disabling client side caching is possible, it is rare that we see this configuration at any of our customers. If this configuration is used in parts of the organization and there are worries about network traffic or Exchange server load, please keep this in mind. Depending on the configuration, Spirion may be unable to perform a search if Outlook is not configured to "Use Cached Exchange Mode."