By default SLmail has unlimited mailbox size (actual size depends on system resources). There are three levels of quotas:
Global --mailbox quota for all domain or user accounts on the server.
Domain --mailbox quota for all user accounts in the particular domain.
User --mailbox quota for a specific user.
The quotas have different levels of precedence depending on what is selected. For example, a user specified quota (if enabled) has precedence over its domain quota and the global quota. A domain quota (if enabled) has precedence over the global quota.
The Mailbox Quotas have three "states":
Disabled --no mail traffic across the server.
Enabled --Disk and Grace Quotas enforced.
Unlimited --Disk and Grace Quotas disregarded.
Note: Disabled is not the same as "not enabled". If the Global Quota is set to Disabled , NO mail will cross the server. It is suggested that the Global Quota be set to Disabled only for maintenance reasons for short periods of time.
When a new domain or user is added the quotas for these "accounts" is not enabled by default and therefore falls under the global quota. A domain or user quota must be enabled and specified in order to take precedence over the global quota.
There are two quota levels, Disk and Grace. The Disk quota is a "soft" quota in that if the mailbox is nearing this quota and a large message arrives this quota can be exceeded. The Grace Quota is an additional amount added to the Disk Quota that can be used for message "overflow" as in the previous example. If the mailbox size exceeds the sum of the two quotas, the user will have to remove messages from the server before he can receive any additional messages.
Disk Quota set to 10MB, Grace Quota set to 1MB.
User currently has 8.3MB stored in his mailbox and receives a 2.1MB message. The total in the mailbox will exceed the Disk Quota (10.4 vs. 10MB) but the message will be allowed. With 10.4MB in the mailbox, the user receives another 1.4MB message. This will put the mailbox at 11.8MB, which exceeds the sum of the Disk and Grace quota, but this message will be accepted because the mailbox quota does not know the size of the incoming message. Only after the message is in the mailbox and the sum of the quotas is exceeded will additional messages be rejected.
When mail is rejected, it is returned to the sender with a 400 (non fatal) level error stating that the sender should try to resend the message at a later time