On 10 Dec 2017 23:13 -0700, from tuhs at minnie.tuhs.org (Grant Taylor via TUHS):
> Does anyone know of any other similar history discussion mailing
> lists / newsgroups to discuss things like Mainframes or (Open)VMS?

Not a mailing list, but have you considered the Retrocomputing Stack
Exchange?

https://retrocomputing.stackexchange.com/

Many of the questions there currently relate primarily to personal
computers and consoles, but I see no reason why questions about e.g.
historical mainframes would not be welcome.

-- 
Michael Kjörling • https://michael.kjorling.se • michael at kjorling.se
                 “People who think they know everything really annoy
                 those of us who know we don’t.” (Bjarne Stroustrup)