OK - I just tried it again and here's what I got. Switching back to beta 9 fixes it so whatever you changed it started in rc1.
dovecot: Jul 01 11:50:52 Info: auth(default): passwd-file(tenacity@sturdywench.com,127.0.0.1): unknown user dovecot: Jul 01 11:50:54 Info: auth(default): client out: FAIL 9 user=tenacity@sturdywench.com dovecot: Jul 01 11:50:54 Info: auth(default): client in: AUTH 10 PLAIN service=IMAP secured lip=127.0.0.1 rip=127.0.0.1 resp=AHRlbmFjaXR5QHN0dXJkeXdlbmNoLmNvbQBsYWNleTEyMw== dovecot: Jul 01 11:50:54 Info: auth(default): pam(tenacity@sturdywench.com,127.0.0.1): pam_authenticate() failed: Authentication failure dovecot: Jul 01 11:50:54 Info: auth(default): passwd-file(tenacity@sturdywench.com,127.0.0.1): unknown user dovecot: Jul 01 11:50:54 Info: auth(default): client in: AUTH 11 PLAIN service=IMAP lip=69.50.231.8 rip=24.9.45.107 resp=AGxhcnJ5QGxlc3NpZy5vcmcAbDEzMDMwMGxc dovecot: Jul 01 11:50:54 Info: auth(default): pam(larry@lessig.org,24.9.45.107): pam_authenticate() failed: Authentication failure dovecot: Jul 01 11:50:54 Info: auth(default): passwd-file(larry@lessig.org,24.9.45.107): unknown user dovecot: Jul 01 11:50:56 Info: auth(default): client out: FAIL 10 user=tenacity@sturdywench.com dovecot: Jul 01 11:50:56 Info: auth(default): client out: FAIL 11 user=larry@lessig.org dovecot: Jul 01 11:50:56 Info: imap-login: Aborted login: user=<tenacity@sturdywench.com>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, secured dovecot: Jul 01 11:50:57 Info: auth(default): client in: AUTH 12 PLAIN service=IMAP secured lip=127.0.0.1 rip=127.0.0.1 dovecot: Jul 01 11:50:57 Info: auth(default): client out: CONT 12 dovecot: Jul 01 11:50:57 Info: auth(default): client in: CONT 12 AG1hcmNAcGVya2VsLmNvbQBkYXJtMGs= dovecot: Jul 01 11:50:57 Info: auth(default): pam(marc@perkel.com,127.0.0.1): pam_authenticate() failed: Authentication failure dovecot: Jul 01 11:50:57 Info: auth(default): passwd-file(marc@perkel.com,127.0.0.1): unknown user dovecot: Jul 01 11:50:58 Info: auth(default): client out: FAIL 12 user=marc@perkel.com dovecot: Jul 01 11:50:58 Info: auth(default): client in: AUTH 13 PLAIN service=IMAP lip=69.50.231.8 rip=24.63.194.47 resp=AHBhdEBhbWJyeW5ldC5jb20AcjBzZWJ1ZA== dovecot: Jul 01 11:50:58 Info: auth(default): pam(pat@ambrynet.com,24.63.194.47): pam_authenticate() failed: Authentication failure dovecot: Jul 01 11:50:59 Error: auth(default): passwd-file /etc/vmail/shadow.ambrynet.com: User pat has invalid GID -1 dovecot: Jul 01 11:50:59 Error: auth(default): passwd-file /etc/vmail/shadow.ambrynet.com: User admin has invalid GID -1 dovecot: Jul 01 11:50:59 Error: auth(default): passwd-file /etc/vmail/shadow.ambrynet.com: User notify has invalid GID -1 dovecot: Jul 01 11:50:59 Error: auth(default): passwd-file /etc/vmail/shadow.ambrynet.com: User dev has invalid GID -1 dovecot: Jul 01 11:50:59 Error: auth(default): passwd-file /etc/vmail/shadow.ambrynet.com: User donor has invalid GID -1 dovecot: Jul 01 11:50:59 Error: auth(default): passwd-file /etc/vmail/shadow.ambrynet.com: User ecomm has invalid GID -1 dovecot: Jul 01 11:50:59 Error: auth(default): passwd-file /etc/vmail/shadow.ambrynet.com: User gmail has invalid GID -1 dovecot: Jul 01 11:50:59 Error: auth(default): passwd-file /etc/vmail/shadow.ambrynet.com: User news has invalid GID -1 dovecot: Jul 01 11:50:59 Error: auth(default): passwd-file /etc/vmail/shadow.ambrynet.com: User shop has invalid GID -1 dovecot: Jul 01 11:50:59 Error: auth(default): passwd-file /etc/vmail/shadow.ambrynet.com: User travel has invalid UID -1 dovecot: Jul 01 11:50:59 Error: auth(default): passwd-file /etc/vmail/shadow.ambrynet.com: User bank has invalid UID -1 dovecot: Jul 01 11:50:59 Error: auth(default): passwd-file /etc/vmail/shadow.ambrynet.com: User adc has invalid GID -1 dovecot: Jul 01 11:50:59 Error: auth(default): passwd-file /etc/vmail/shadow.ambrynet.com: User avn has invalid GID -1 dovecot: Jul 01 11:50:59 Error: auth(default): passwd-file /etc/vmail/shadow.ambrynet.com: User comics has invalid GID -1 dovecot: Jul 01 11:50:59 Info: auth(default): passwd-file /etc/vmail/shadow.ambrynet.com: Read 0 users dovecot: Jul 01 11:50:59 Info: auth(default): passwd-file(pat@ambrynet.com,24.63.194.47): unknown user dovecot: Jul 01 11:51:00 Info: auth(default): client out: FAIL 13 user=pat@ambrynet.com dovecot: Jul 01 11:51:01 Info: auth(default): client in: AUTH 5 PLAIN service=POP3 lip=69.50.231.8 rip=82.35.77.65 resp=AHBhdWxhQGljb21tb25zLm9yZwBkZWl0eTE= dovecot: Jul 01 11:51:01 Info: auth(default): pam(paula@icommons.org,82.35.77.65): pam_authenticate() failed: Authentication failure dovecot: Jul 01 11:51:01 Error: auth(default): passwd-file /etc/vmail/shadow.icommons.org: User paula has invalid GID -1 dovecot: Jul 01 11:51:01 Error: auth(default): passwd-file /etc/vmail/shadow.icommons.org: User counsel has invalid GID -1 dovecot: Jul 01 11:51:01 Error: auth(default): passwd-file /etc/vmail/shadow.icommons.org: User mia has invalid GID -1 dovecot: Jul 01 11:51:01 Error: auth(default): passwd-file /etc/vmail/shadow.icommons.org: User info has invalid GID -1 dovecot: Jul 01 11:51:01 Error: auth(default): passwd-file /etc/vmail/shadow.icommons.org: User heather has invalid GID -1 dovecot: Jul 01 11:51:01 Error: auth(default): passwd-file /etc/vmail/shadow.icommons.org: User daniela has invalid GID -1 dovecot: Jul 01 11:51:01 Error: auth(default): passwd-file /etc/vmail/shadow.icommons.org: User registration has invalid GID -1 dovecot: Jul 01 11:51:01 Error: auth(default): passwd-file /etc/vmail/shadow.icommons.org: User keller has invalid GID -1 dovecot: Jul 01 11:51:01 Error: auth(default): passwd-file /etc/vmail/shadow.icommons.org: User pete has invalid GID -1 dovecot: Jul 01 11:51:01 Info: auth(default): passwd-file /etc/vmail/shadow.icommons.org: Read 0 users dovecot: Jul 01 11:51:01 Info: auth(default): passwd-file(paula@icommons.org,82.35.77.65): unknown user dovecot: Jul 01 11:51:02 Info: auth(default): client out: FAIL 5 user=paula@icommons.org dovecot: Jul 01 11:51:02 Info: pop3-login: Aborted login: user=<paula@icommons.org>, method=PLAIN, rip=82.35.77.65, lip=69.50.231.8