This is a bit of mailing list administratativia.†
More specifically, many of you may have recently been unsubscribed to the
Code4Lib mailing list, and this is/was apparently a feature of our mailing list
software — LISTSERV. Even more specifically, many of us have been using Gmail
accounts or have Google hosting our SMTP servers. In either case, Google
servers have been more strict about what gets passed on as “not spam”, and our
list’s domain has yet to meet the challenge. The “challenge” includes a mixture
of Domain Name Server (DNS) configurations, various types of signatures in the
email headers, etc. For more detail, see a Google FAQ.  The good people at
CLIR/DLF (Wayne Graham, specifically) are on the case, and the whole thing may
be resolved in a week or two.
† Apparently “administratativia” is not a real word, but what the heck.
 FAQ - http://bit.ly/2cTYA5E
Specifically Yours, Eric Morgan