size <":over" / ":under"> <limit: number>
The "size" test deals with the size of a message. It takes either a tagged argument of ":over" or ":under", followed by a number representing the size of the message.
If the argument is ":over", and the size of the message is greater than the number provided, the test is true; otherwise, it is false.
If the argument is ":under", and the size of the message is less than the number provided, the test is true; otherwise, it is false.
Exactly one of ":over" or ":under" must be specified, and anything else is an error.
The size of a message is defined to be the number of octets (bits) from the initial header until the last character in the message body.
Note that for a message that is exactly 4,000 octets, the message is neither ":over" 4000 octets nor ":under" 4000 octets.
Core : Requires no import statement
RFC3028