Quotas can be set for specific users or domains and can be set in terms of number of messages or number of bytes. It can also be set for specific folders and message types. Message type quotas allow you to specify limits for message type. For example, voice mail and email. Folder quotas set limits to the size of a user's folder in bytes or messages. For example, a quota can be set on the Trash folder. Messaging Server allows you to set default quotas for domains and users as well as customized quotas.
Once a quota is set, how the system responds to users or domains that are either over quota or approaching the quota is also configurable. One response is to send users an over quota notification. Another response is to halt delivery of messages into the message store when quota is exceeded. This is called quota enforcement and usually occurs after a specified grace period. A grace period is how long the mailbox can be over the quota before enforcement occurs. If message delivery is halted due to over quota, incoming messages remain in the MTA queue until one of the following occurs:
The size or number of the user’s messages no longer exceeds the quota, at which time the MTA delivers the messages.
The undelivered message remains in the MTA queue longer than the specified grace period, at which time messages are returned to sender. (See 188.8.131.52 To Set a Grace Period).
The message has remained in the message queue longer than the maximum message queue time. This is controlled by the notices MTA channel keyword (see 10.10.4.3 To Set Notification Message Delivery Intervals).
For example, if your grace period is set for two days, and you exceed quota for one day, new messages continue to be received and held in the message queue, and delivery attempts continue. After the second day, the messages bounce back to the sender.
Disk space becomes available when a user deletes and expunges messages or when the server deletes messages according to expiration policies established (see 20.9 To Set the Automatic Message Removal (Expire and Purge) Feature).
To support unified messaging requirements, Messaging Server provides the ability to override quota limitations imposed by the message store. This guarantees the delivery of messages that have been accepted by certain agents, namely telephony application servers (TAS). Messages accepted by a TAS can be routed through a special MTA channel that ensures the message is delivered to the store regardless of quota limits. This is a fairly esoteric usage, but can be used to telephony applications. For more information about configuring an TAS channel, contact your Sun messaging representative.
Quota by message type is useful for telephony applications that use unified messaging. For example, if a mix of messages, say text and voice mail, is stored in a user's mailbox, then the administrator can set different quotas for different types of messages. The user's email can have one quota, and their voice mail can have a different quota.