Original URL: http://help.hardhathosting.com/question.php/179
Max Address Book Size: This is the maximum size(In kilobytes) that a user's address book can grow to. This avoids a user filling up your server's hard drive space by spamming garbage address book entries.
We recommend 1000 kilobytes
Folder Quota: Once a user's saved email messages spools meet or exceed this size (in KB), no future messages will be able to be sent to any folder other than TRASH, where they will be immediately deleted, until space is freed.
We recommend 15000 KB
Attachment Limit: This is the limit on the size of attachments (in MB). Large attachments can significantly drain a server's resources during the encoding process. Note that this affects outgoing attachment size only, and will not prevent users from receiving messages with large attachments.
We recommend 5 MB
Session Timeout: This indicates how many minutes of inactivity pass before a session is considered timed out and the user needs to log in again. Make sure this is big enough that a user typing a long message won't get logged out automatically while typing!
We recommend 180 minutes
Number of Headers: This indicates the maximum number of headers to display to a user at a time. Keep this number reasonable to ensure fast load times for slow connection users.
We recommend 10 emails to display