Many of the configurations available in global settings can be made elsewhere in Exchange. Message encoding, for example, can be configured in an individual user's mailbox, on a Post Office Protocol version 3 (POP3) virtual server for a group of users, and globally for all users. For this reason it is important to understand the relationship between defaults set on different Exchange objects.
To accommodate exceptions in an organization, global settings only apply when all other defaults or limits are disabled. Therefore, mailbox settings supercede global settings.
For user mailbox properties, Use default limit is the default selection for many of the delivery options. When Use default limit is selected, the mailbox will always defer to the global settings. If the corresponding global setting is No limit, no limits are imposed.
For many message delivery settings, there are situations where no default limits exist, either globally or at the mailbox level. When no default limits exist, delivery defaults sometimes fall to the Simple Mail Transfer Protocol (SMTP) virtual server. To use the example of message size limits, SMTP virtual server message size limits apply to incoming messages only. This means SMTP virtual servers will refuse messages from clients or other servers that exceed the specified limit. Once the SMTP virtual server accepts the message, the SMTP virtual server will try to deliver the message regardless of size.
Note When no limit is set on the virtual server, it will accept any size message.
For example, if a 100-kilobyte message is sent over the Internet to an Exchange organization, it must first be accepted by an SMTP virtual server. If the virtual server's size limit is more than 100 KB, or if there is no size limit imposed, the message is accepted. If the Exchange organization has a global incoming message size limit of 80 KB, the delivery will fail. The SMTP virtual server will eventually return a non-delivery report (NDR) to the sender. If there is one mailbox in the organization that can receive messages up to 120 KB, that user will be the only person to receive the message.
Outgoing messages can work the same way. If there are no outgoing message size limits imposed in an organization, either globally or on a per-user basis, a user can try to send a message of 1,000 KB. A problem may arise when the SMTP virtual server imposes a message size limit of 500 KB. Even though the mailbox limit allows a user to send such a message, the SMTP virtual server will not accept it, because of its own message size limit. The message will not be delivered.