It is self explanatory, if there had been a user dovecot, but there wasn't. After the install fails there is a user dovecot but no group.
Code:
$ pw show user -a | grep dove
[1] 13303 done pw show user -a |
13304 exit 1 egrep --colour=auto dove
$ pw show group -a | grep dove
[1] 13305 done pw show group -a |
13306 exit 1 egrep --colour=auto dove
$ sudo portmaster mail/dovecot2
...
...
===> Installing for dovecot-2.2.4
===> Generating temporary packing list
===> Checking if mail/dovecot2 already installed
===> Creating users and/or groups.
Creating group `dovecot' with gid `143'.
Creating group `dovenull' with gid `144'.
Creating user `dovecot' with uid `143'.
pw: user 'dovecot' already exists
*** [create-users-groups] Error code 74
Stop in /usr/ports/mail/dovecot2.
*** [install] Error code 1
Stop in /usr/ports/mail/dovecot2.
===>>> Installation of dovecot-2.2.4 (mail/dovecot2) failed
===>>> Aborting update
===>>> Killing background jobs
Terminated
===>>> You can restart from the point of failure with this command line:
portmaster <flags> mail/dovecot2
===>>> Exiting
[1] 13964 exit 1 sudo portmaster mail/dovecot2
sudo portmaster mail/dovecot2 291.95s user 78.22s system 83% cpu 7:25.25 total
$