cyrus not listening to any ipv4 port

[admin]

Hi
after a system update on centos 6.7 final (2.6.32-573.3.1.el6.x86_64) and a reboot cyrus (2.3.16-13) does not listen anymore on any ipv4 port.
netstat -tulpen says:
tcp        0      0 :::143                      :::*                        LISTEN      0          16131949   20054/cyrus-master
tcp        0      0 :::993                      :::*                        LISTEN      0          16131956   20054/cyrus-master

That is ipv6 as far as i know.

udp        0      0 0.0.0.0:143                 0.0.0.0:*                               0          10484      1407/portreserve
udp        0      0 0.0.0.0:993                 0.0.0.0:*                               0          10486      1407/portreserve

What does "portreserve" mean?

Nmap from remote:
nmap 85.25.155.7
22/tcp   open     ssh
25/tcp   open     smtp
80/tcp   open     http
389/tcp  open     ldap
443/tcp  open     https
8443/tcp open     https-alt

Nmap run locally from server
nmap 85.25.155.7 (or localhost)
rDNS record for 85.25.155.7: puck1171
Not shown: 993 closed ports
PORT     STATE SERVICE
22/tcp   open  ssh
25/tcp   open  smtp
80/tcp   open  http
389/tcp  open  ldap
443/tcp  open  https
3306/tcp open  mysql
8443/tcp open  https-alt

The cyrus.conf is:
SERVICES {
  # add or remove based on preferences
  imap          cmd="imapd" listen="imap" prefork=5
  #imaps         cmd="imapd -s" listen="imaps" prefork=5
  imaps         cmd="imapd -s" listen="[85.25.155.7:]imaps" proto=tcp4 prefork=5
  pop3          cmd="pop3d" listen="pop3" prefork=3
  pop3s         cmd="pop3d -s" listen="pop3s" prefork=1
  sieve         cmd="timsieved" listen="sieve" prefork=0
  lmtpunix      cmd="lmtpd" listen="/var/lib/imap/socket/lmtp" prefork=1
}
(cyrus-imapd restarted, several imapd/pop3d proesses are running)
I am lost at this point and do not know what to check next. Any help is highly appreciated.
The log reports some "auxpropfunc error invalid parameter supplied" messages, but these are subject to authentification, right?

Malte