[ch] change in list posting policy

[Joe Touch]

Hi, all,

Regrettably, we have now enabled 'subscriber-only' posting on the 
computer-history mailing list.

Although the amount of spam on this list has been kept fairly low 
overall, the contamination of the list archives, together with the 
increasingly common prevalence of this policy on other lists, has caused 
us to implement it here.

Please let us know if this causes any complications when you try to post.

Joe Touch & Bob Braden