This note does not concern the main OCaml email list, which continues to be available through https://sympa.inria.fr/sympa/arc/caml-list/
The lists.ocaml.org e-mail service has been going through a rough time in the past few years, with vast swathes of spam regularly hitting our ingress email server and require manual unblocking every time. It was set up back in 2012 as an augmentation of the main OCaml mailing list and really helped with some big projects in the early days (the design of and migration to ppx from camlp4, for example). However, in the intervening years e-mail has reduced in importance as a primary community communication mechanism (as evidenced, for example, in this forum).
With the latest spam surge, I’ve moved the service into read-only mode with all the mailboxes and archives still available on the website, but with mail delivery and list creation/admin disabled. All existing links should continue to work to historical links online without change. The only mailing list on there that was still active to my knowledge is the opam-commits cron list, which will be replaced by an ocurrent-based deployer for that website shortly.
I hope to bring e-mail back to ocaml.org sometime in 2022, as it’s an important communications medium that is highly accessible. One challenge is spam, and another is the inflexibility of GNU Mailman and its upgrade mechanism (essentially a manual process from 2 to 3). Therefore, if there is anyone in the community interested in building a simple e-mail list manager in OCaml, that would be of interest 
