Use Cached mode for shared mailboxes? RRS feed

  • Question

  • - We are running Exchange 2007.

    - Clients range from Outlook 2003 thru 2013.

    - Many mailboxes are HUGE, between 10gb and 80gb.

    - For business purposes the majority of our mailboxes are shared by multiple users and are generally in online and not cached mode due to the size. The user accounts have an internal only mailbox in addition to the shared external access mailbox and are configured to have full access multiple mailboxes with the shared mailbox as their primary.

    -In some cases the users AD profile is set to use only the shared email as primary and have no other mailbox configured for them.

    -Many users have full permission to other users mailboxes set up in their outlook profile just to be sure that no email is missed by anyone. It is not uncommon for a user to have 3 or 4 mailboxes available in their folder list.

    -we have a lot of automatic forwarding of messages so that supervisors and managers receive all email that is sent to those below them.

    Is there any advantage to using cached mode in this environment? What are the issues that will occur if the shared mailboxes are configured to cached mode on the clients? I could foresee frequent sync conflicts and corrupt OST files. Am I correct? Management wants to remove remove any the local mailboxes that are unused and configure the users AD account to default to the common shared mailboxes.

    Any suggestions on how to streamline the configuration of this sort of environment? We are looking to move to Exchange 2010 or maybe 2013 in the near future if that helps.



    just another Steve

    Saturday, September 21, 2013 3:45 PM


  • From your description I'd probably avoid using cached mode in your situation most of the time. It can make things a lot faster since everything is being done locally, but as you say it does have issues if you have large mailboxes like yours.

    In my experience, and from what I've read from other people, the larger the mailbox is the more chance you have that you'll see issues with the local cache become corrupted, so you'll then have to clear it and start again. The rule of thumb I generally use is to avoid anything larger than 10GB for a cached mailbox. Outlook can handle it, but I think almost every single instance of someone having a corrupt .ost file has been when their mailbox has been 10GB+ in size.

    The mixture of Outlook versions complicates things as well, as different versions handle caching differently, with some caching the data in additional mailboxes, and some not.

    The good news is that Outlook 2013 allows you to set how much of the mailbox to cache, so you can for instance just get it to cache the last months worth of mail rather than the entire mailbox. Then your more recent messages are accessed quickly, the older messages continue to be retrieved from the server, and you avoid having massive .ost files which will generate problems.

    So for those users that have Outlook 2013 it might well be beneficial to use it. For the rest it very much depends on the size of the mailbox they're connecting to, so if it's that 80GB mailbox then definitely not.

    Saturday, September 21, 2013 6:26 PM