Sun Java System Messaging Server 6 2005Q4 MTA Developer's Reference

item_length

When the item code has an associated string value, this field optionally provides the length in bytes of the string, not including any NULL terminator. If a value of zero (0) is supplied, then the string pointed to by item_address must be NULL terminated, so that mtaSend() can automatically determine the string’s length.

When the item code has an associated integer value, this field supplies that value.