Copied from Microsoft;
Microsoft Exchange Server has a maximum limit of 32 kilobytes (KB) for
storage of rules. Rules vary in size, but some rules can be significantly
larger when they involve multiple recipients in a forward action. Each
recipient can add up to 500 bytes to the size of the rule. As a rough
estimate, the simplest rules take from 200 to 500 bytes. Rules involving
recipients add approximately 500 bytes per recipient. A rule that forwards a
message to five recipients, can be over 3 KB in size.
When rules involve several recipients, it is best to create a distribution
list and use the distribution list as the recipient. This allows more rules
to be created before reaching the 32 KB rule limit. Personal distribution
lists are not allowed in rules; only distribution lists created through the
Microsoft Exchange Server administration program.
