All communication should be in public wherever possible:
#guadec-org on irc.gnome.org - public channel, also used for IRC meetings
guadec-list@gnome.org (archives) - public mailing list
But sensitive matters which are best kept private do occasionally arise:
guadec-organization@gnome.org (archives) - private mailing list for the core organising team
There are also some aliases for the mailing lists:
You may also want to communicate with the general public:
https://twitter.com/guadec (owned by guadec-organization@gnome.org)
https://www.youtube.com/user/GUADEC (owned by guadec-organization@gnome.org)
If you are an attendee, you can use…
#guadec on irc.gnome.org - public channel for attendees