Please change the DNS lookup = defaultdomain process, and use defaultdomain as the default domain.

[josh at endries.org]

I fixed this issue, created this patch:

mail# cat patch-imap::global.c
--- imap/global.c.orig  2009-07-08 13:41:29.000000000 -0400
+++ imap/global.c       2009-07-08 13:41:36.000000000 -0400
@@ -391,7 +391,8 @@
                     !(config_defdomain &&  
!strcasecmp(config_defdomain, domain+1))) {
                     /* append the domain from our IP */
                     snprintf(buf, sizeof(buf), "%s@%s", user, domain+1);
-                   user = buf;
+// Added by Josh to prevent appending DNS domain on unqualified user IDs.
+//                 user = buf;

                     if (domain_from_ip) *domain_from_ip = 1;
                 }

This effectively prevents Cyrus from appending the domain name from  
DNS on to the user ID if the ID is unqualified. I tested it and it  
works for me, other virtual domain accounts (user at domain) are  
unaffected.

Josh