[Dovecot] antispam_plugin prevents IMAP login (error 3) [Dovecot 2.0.19]

[dof at projektfabrik.com]

Hi everybody,

trying to get the Dovecot antispam_plugin to work and I must be doing 
something wrong, because as soon as it is enabled with a certain 
backend, imap logins do not work anymore (the session is immediately 
closed after a successful login). Interestingly, pipe and spool2dir are 
working (that is, the session won't be closed), dspam-exec and 
crm114-exec are not. If this happens, mail_debug output is as follows:

   imap-login: Login: user=<dof>, method=PLAIN, rip=127.0.0.1, 
lip=127.0.0.1, mpid=10420, secured
   imap: Debug: Loading modules from directory: /usr/lib/dovecot/modules
   imap: Debug: Module loaded: 
/usr/lib/dovecot/modules/lib20_autocreate_plugin.so
   imap: Debug: Module loaded: 
/usr/lib/dovecot/modules/lib20_fts_plugin.so
   imap: Debug: Module loaded: 
/usr/lib/dovecot/modules/lib21_fts_squat_plugin.so
   imap: Debug: Module loaded: 
/usr/lib/dovecot/modules/lib90_antispam_plugin.so
   imap(dof): Debug: Effective uid=23244, gid=8, 
home=/var/spool/dovecot/userdata/dof
   imap(dof): Debug: Home dir not found: /var/spool/dovecot/userdata/dof
   master: Error: service(imap): child 10420 returned error 3

Without the plugin I get:

   imap-login: Login: user=<dof>, method=PLAIN, rip=127.0.0.1, 
lip=127.0.0.1, mpid=10469, secured
   imap: Debug: Loading modules from directory: /usr/lib/dovecot/modules
   imap: Debug: Module loaded: 
/usr/lib/dovecot/modules/lib20_autocreate_plugin.so
   imap: Debug: Module loaded: 
/usr/lib/dovecot/modules/lib20_fts_plugin.so
   imap: Debug: Module loaded: 
/usr/lib/dovecot/modules/lib21_fts_squat_plugin.so
   imap(dof): Debug: Effective uid=23244, gid=8, 
home=/var/spool/dovecot/userdata/dof
   imap(dof): Debug: Home dir not found: /var/spool/dovecot/userdata/dof
   imap(dof): Debug: fs: root=/var/spool/dovecot/mail/dof, index=, 
control=, inbox=/var/spool/dovecot/mail/dof/INBOX, alt=
   imap(dof): Debug: Namespace : Using permissions from 
/var/spool/dovecot/mail/dof: mode=0755 gid=-1


Hopefully this is just a configuration problem. I tried the plugin in 
the Ubuntu repository (I'm using LTS 12.04) and even checked out the 
source from git and compiled it myself, but to no avail.


Thanks a lot in advance and best regards,
Florian


-------------------

dovecot -n output:

auth_cache_size = 128 k
auth_cache_ttl = 20 mins
auth_failure_delay = 10 secs
auth_mechanisms = plain login
disable_plaintext_auth = no
login_greeting = Projektfabrik IMAP ready.
mail_gid = mail
mail_home = /var/spool/dovecot/userdata/%u
mail_location = 
maildir:/var/spool/dovecot/mail/%u:INBOX=/var/spool/dovecot/mail/%u/INBOX:LAYOUT=fs
mail_uid = dovemail
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope 
encoded-character vacation subaddress comparator-i;ascii-numeric 
relational regex imap4flags copy include variables body enotify 
environment mailbox date
passdb {
   args = /etc/dovecot/dovecot-ldap.conf
   driver = ldap
}
plugin {
   antispam_backend = dspam-exec
   antispam_dspam_binary = /usr/bin/dspam
   antispam_signature = X-DSPAM-Signature
   antispam_signature_missing = error
   antispam_spam = Spam
   antispam_trash = trash;Trash;Deleted Items; Deleted Messages
   autocreate = INBOX/Sent Mail
   autocreate2 = INBOX/Spam
   autocreate3 = INBOX/Trash
   autosubscribe = INBOX/Sent Mail
   autosubscribe2 = INBOX/Spam
   autosubscribe3 = INBOX/Trash
   fts = squat
   sieve = /var/spool/dovecot/sieve/%u/defaultbc
   sieve_before = /etc/dovecot/sieve/spam.sieve
   sieve_dir = /var/spool/dovecot/sieve/%u
}
protocols = imap pop3 sieve
service auth {
   unix_listener /var/spool/postfix/private/dovecot-auth {
     group = postfix
     mode = 0600
     user = postfix
   }
   unix_listener auth-userdb {
     mode = 0600
     user = dovemail
   }
   user = dovenull
}
service imap-login {
   inet_listener imap {
     address = localhost
     port = 143
   }
   inet_listener imaps {
     address = localhost XX.XXX.XX.XXX
     port = 993
   }
   service_count = 1
   user = dovenull
}
service managesieve-login {
   inet_listener sieve {
     address = localhost
     port = 2000
   }
   service_count = 1
   user = dovenull
}
service pop3-login {
   inet_listener pop3 {
     address = localhost
     port = 110
   }
   inet_listener pop3s {
     address = XX.XXX.XX.XXX
     port = 995
   }
   service_count = 1
   user = dovenull
}
ssl_ca = </etc/ssl/dovecot/cacert.pem
ssl_cert = </etc/ssl/dovecot/cert.pem
ssl_key = </etc/ssl/dovecot/key.pem
protocol imap {
   imap_client_workarounds = tb-extra-mailbox-sep
   mail_plugins = antispam autocreate fts fts_squat
}
protocol pop3 {
   pop3_client_workarounds = outlook-no-nuls oe-ns-eoh
   pop3_lock_session = yes
}
protocol lda {
   mail_fsync = optimized
   mail_plugins = sieve
   postmaster_address = postmaster at projektfabrik.com
}