On Sat, 24 Feb 2001 12:58:49 +0200, Erwin Weiblen <[log in to unmask]>
wrote:

>Is it possible to add a serial number to the mails, 

This is automatically done with Digests, but not with single messages.

>e.g. by inserting
>a header line "X-Number: ..." ?

There is no such header line so this won't work.