geeky question on read/unread mail

[Globe Trotter]

Hi,

How do all these mailers tell whether an e-mail has actually been read or not?
By that, I mean, how does pine (or sylpheed or whatever) find out if an e-mail
has actually been read? Please note that I am not asking how they indicate
whether an e-mail has been read or not (this is different for different
mailers) but how to they find out whether each e-mail in the folder should be
classified as unread or read. 

This may well depend on format (MH or mbox or the like) but I still wonder how
this is settled.

Thanks and best wishes!



		
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