The most important resource for developers are the project mailing lists.
The current set of mailing lists are as follows:
libc-announce: The libc-anounce list is used to inform users and developers of upcoming releases and anouncements.
libc-help: The libc-help list is intended for all glibc questions including build problems, C library usage, and more. No question about glibc is ever wrong on this list.
libc-alpha: The libc-alpha list is for the discussion of glibc development. Please do not ask for build help on this list.
libc-locales: The libc-locales mailing list is used for discussing locale specific changes and patches to glibc.
libc-stable: The libc-stable mailing list is used to discuss changes backported to stable branches. The list also receives git commit traffic for stable release branches. Distribution developers can subscribe to the list to track backports and determine if their own distribution branches need to be rebased and or if the stable release branch they depend upon needs backports.
libc-testresults: The libc-testresults mailing list is intended to centrally collect the test results of developer builds.
The deprecated set of mailing lists are as follows:
libc-hacker: The libc-hacker list was a closed list, and is no longer used. It is still possible to look at the archives of the list.
libc-ports: The libc-ports mailing list is no longer used. It was previously used to discuss the ports add-on, but after 2.19 it was merged directly into the core project. It is still possible to look at the archives of the list.
Mail archives are also available by anon-ftp in mbox formatted files.