First, read all the USENET newsgroups with "sun" in their name :-)
1) The Florida SunFlash is a "closed" mailing list for Sun owners. It contains mostly press releases from Sun and third-party vendors. This list contains information on conferences such as the Solaris Developer's Conference as well. It is normally distributed regionally - to find out about a mail point in your area, or for other information send mail to info-sunflash@Sun.COM.
Subscription requests should be sent to sunflash-request@Sun.COM. Archives are on solar.nova.edu, ftp.uu.net, sunsite.unc.edu, src.doc.ic.ac.uk and ftp.adelaide.edu.au
2) The Sun Managers list is an unmoderated mailing list for emergency-only requests. Subscribe and listen for a while, and read the regularly-posted Policy statement BEFORE sending mail to it, and to get a feel for what kinds of traffic it carries. Send a message with "subscribe sun-managers" in the body to majordomo@sunmanagers.ececs.uc.edu to subscribe.
3) The solaris x86 list. Subscribe/unsubscribe by sending a message with subscribe/unsubscribe in the BODY of the message to solaris-x86-request@mlist.eis.com. A digested version of the list is also available. To subscribe send an email message to solaris-x86-digest-request@mlist.eis.com. There's also an archive of this list.
4) The Sun Security Bulletin announcement mailing list. Low volume, announcement only list. Subscribe by mailing security-alert@sun.com with subject "SUBSCRIBE cws user@some.host"