O.K., you found it. Here it comes :)
telnet localhost 2000 Trying 127.0.0.1… Connected to localhost.localdomain. Escape character is '^]'. "IMPLEMENTATION" "Cyrus timsieved v2.2.12-Gentoo" "SASL" "NTLM LOGIN PLAIN DIGEST-MD5 CRAM-MD5" "SIEVE" "fileinto reject envelope vacation imapflags notify subaddress relational comparator-i;ascii-numeric regex" "STARTTLS" OK
Seems like Gentoo's cyrus timesieved is listening there :) Thanks. How do I reconfigure JOnAS to another port?