Outlook gal not updating in cached mode

Various Microsoft documents will vary between that and up to 500 milliseconds, and your own users’ experiences will ultimately decide what is good enough, but with anything over 100 milliseconds Outlook starts to pop notification bubbles that it has lost connectivity to Exchange.That usually generates helpdesk calls, and nobody likes those.

Cached mode, which first came out with Microsoft Outlook 2003, keeps a local copy of the user’s mailbox stored on the hard drive as an OST file.

Running in cached mode, the Outlook client looks to the local OST file for all access, including reads and searches, while a separate process checks for new mail on the server and syncs data to the local cache.

With Office 365 in particular, Microsoft will not prevent you from using online mode, but if performance is poor and you call support, they will instruct you to use cached mode.

For the rest of you, consider the following – if you do any of these, online mode may provide the better experience for your users: Ultimately, I tell all my customers to use cached mode, and if they cannot for any reason, to use OWA instead of Outlook.

You should use cached mode anytime a user must access their mail without network connectivity, such as users who travel.

You should also use it for any users in an office with intermittent network connectivity, or whose network latency between client and server is typically high, like those with satellite or radio-based connectivity.

For Office 365 or other hosted Exchange customers, the answer is easy – use cached mode.

The Exchange CAS server is not local to you, so you will have higher latency and cached mode will accommodate this.

As a rule of thumb, I consider 100 milliseconds to be the maximum latency for online mode.

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