Server 2012 R2, disk quota vs user quota

Take a look at the quota command here:

http://linux.die.net/man/1/quota

quota

For example:

quota -u user1

System response:

Disk quotas for user user1 (uid 501):
     Filesystem  blocks   quota   limit   grace files   quota   limit  grace    
     /dev/hda6     992   50000   55000              71   10000   11000

quota report

Report on all users over quota limits:

quota -q

Quota summary report:

repquota -a

Report for user quotas on device /dev/hda5
Block grace time: 7days; Inode grace time: 7days
                    Block limits                File limits
User            used    soft    hard  grace    used  soft  hard  grace
----------------------------------------------------------------------
root      -- 4335200       0       0         181502     0     0
bin       --   15644       0       0            101     0     0
...
user1     --    1944       0       0            120     0     0    

No limits shown with this user as limits are set to 0.

This is a "length of a piece of string" situation - it depends a lot on the amount of mail and the content of it (all small simple text messages, or do your users regularly send and receive large attachments?).

Your best bet is to have look at recent mail patterns for a sample of users, set your base quota by that multiplied by a small factor.

Two rules of thumb for mail quotas:

1. One size does not fit all, so don't give every user in all departments 4Gb just because the users in the art/marketing department need that much for all the large images they transfer by mail
2. Increasing a user's quota if/when they need it is a lot easier than decreasing it if they don't (they'll moan about losing something, even if they don't need it!) so set the quotas to a reasonable but not over-the-top value and make sure the server(s) send alerts (to the user, your mail admins, or both) when an account hits, say, 90% of quota.

4Gb is certainly too much as a general quota - I have over 18 months worth of mail in less than 256Mb on our current system (we kept the old mail server for archive purposes instead of migrating old data over) and I'm sure many people need less than I unless you are archiving mail for a long time. 1Gb is more realistic, but may still be too much as your base quota for everyone.

As well as considering the volume of allocated space for the live mail stores, remember that you need to allocate enough resource to backups of this data.

And if your users are sending large objects by mail internally (I've seen people send 10s of Mb to everyone in a company address book even though only a few people actually needed the documents), which could result in big mailboxes over time, you should at least consider encouraging them to use a more special purpose document sharing system - this might be easier to manage size wise, could allow useful things like revision/signoff control and other workflow helpers, and might be easier to backup in a way that makes restoring individual documents less work.