https://xsdk.info/faq/ suggests sending e-mail to: [xsdk-dev@listserv.llnl.gov]. However this gives:
You are not authorized to send mail to the XSDK-DEV list from your email account. You might be authorized to post to the list from another account, or perhaps when using another mail program configured to use a different email address. However, LISTSERV has no way to associate this other account or address with yours. If you need assistance or if you have any questions regarding the policy of the XSDK-DEV list, please contact the list owners at XSDK-DEV-request@LISTSERV.LLNL.GOV.
Reported-by: @bernhold