What are the Outlook 2007 client message header limits?

I can't seem to find an answer on this. I need to know what the maximum message header size is for on an Outlook 2007 client?  All the answers I find seem to point to setting the maximum number of recipeints on the exchange side. I can see this with the get-transportconfig command.

But my question is:  Is there also an Outlook 2007 client limitation as to how many recipients you can include in the header portion of a message?  Or is there a size limit on the header size?

Please advise.

Thanks

ExchangeGuru