9. The method as claimed in claim 1 , further comprising: receiving a message having a message header of header names; converting the header names to canonical keys; and building a message header list for the message of the canonical keys.
9. The method as claimed in claim 1 , further comprising: receiving a message having a message header of header names; converting the header names to canonical keys; and building a message header list for the message of the canonical keys. 10. The method as claimed in claim 9 , wherein converting header names further comprising: searching the header name directly in the mapping; and if found, getting the associated value; if not found, converting the header name to lower-case and searching the mapping; if found, adding the new representation to the mapping for subsequent searches; if not found, adding the header name to the mapping with the new header name as a new canonical key.