Maximum Mailbox Size

Posted on 2006-05-30
Last Modified: 2012-01-27
Is there a limit or a recomended limit for either an Exchange 2000 or 2003 individual mailbox size?
Question by:mulshoefer
    LVL 18

    Accepted Solution


    First, there are no inherent size limits on individual mailboxes.  The main factors that limit mailbox size, practically speaking, are available disk space, backup and restore times, Service Level Agreements, and Outlook performance.  By Outlook performance I’m referring to the latencies experienced by the end user.  
    it's not the size of the mailbox that impacts performance - it is the number of items in the folder or folders that are being accessed on the server.  In particular, performance is largely influenced by the number of items in the most commonly used folders: Calendar, Contacts, Inbox, and Sent Item folder.
    Having a large number of items in a folder will mean than operations in that folder will take longer.  Operations that depend on the number of items in the folder include adding a new column to the view, sorting on a new column, finds and searches.   Many Outlook plug-ins do sorts or searches as they are running, and these requests may overlap with other Outlook MAPI requests, resulting in a poor user experience.
    If you are running in Cached-Mode, (the default mode for Outlook 2003), then client performance can be an issue.  One thing you should do is keep your OST files (the local data cache) free of fragments.  

    I usually recommend no more than about 2500 - 5000 messages in any of the critical path folders.  The critical path folders are the Calendar, Contacts, Inbox, and Sent Item folder. Ideally, keep the Inbox, Contacts and Calendar to 1000 or less.  Other folders, particularly custom folders created by the user, can handle having larger numbers of items without having a broad impact on the user experience .

    LVL 26

    Assisted Solution

    Just make sure the quota on all the mailboxes add up to less than the size of the disk(s) the store is located on. Obviously you'll want to leave yourself some breathing room for more users later or something else we aren't thinking of.

    I run a school of about 100 facutly/staff each with quota's set to warn at 90MB, complain louder at 110MB and limit send/receive at 150MB. Certain people always need more (the CFO and Headmaster accounts are limited around 400MB), so leave some room for the "special" cases. This setup works well for me, might not for you, but hopefully you'll get the idea.
    LVL 3

    Author Comment

    That's how we have ours setup.  I was wondering if there was an official 'limit'  from Microsoft.
    LVL 26

    Expert Comment

    Nope, the default is no quota for any account. I've read about many admins that leave it that way until they run out of disk space or they hit the limit for the store.
    LVL 104

    Assisted Solution

    There is no official word from Microsoft on limits.

    That would be like a car manufacturer telling you how fast you can drive your car. The only limit is its top speed (the size of the Exchange database).

    There is no hard and fast rule either as it depends on so many factors...

    - number of users
    - number of servers
    - amount of disk space
    - regulatory or legal requirements
    - types of messages being sent.

    A 200mb limit might be good for sales people, but marketing or designed who often move around large files might require a larger limit.

    The maximum limit you can set though is 2gb. Anything bigger is unlimited.
    When I deploy limits I always limit down, not open up. The global limit is the largest that anyone can have (is effectively the default) and then users or groups are limited down from that point. It provides a simple safety net in the case of a problem.
    Even if the client isn't using limits, I will often set a global soft limit of 1gb, which puts a check in place in case any mailboxes get out of control. If the mailboxes are small, then it can be set to a hard limit.

    Every company is different - you could decide on a 10mb limit or a 100mb limit.
    Another trick is to have an excellent journaling product to store the email messages as they pass through the server. When the users get used to having that product in place they will keep less email in their live mailbox, safe in the knowledge that they can get the older stuff from the journal system.


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