Users can't use Dovecot IMAP

[John Lewis]

Every time a user logs into Dovcot's IMAP service PAM closes the session immediately after it opens. I would like a user to have a session open long enough to read some emails.

dictator at drakeclasher:~$ sudo dovecot -n                                        
# 2.1.7: /etc/dovecot/dovecot.conf
# OS: Linux 3.14-0.bpo.1-amd64 x86_64 Debian 7.8 
mail_location = maildir:~/Maildir
namespace inbox {
  inbox = yes
  location = 
  mailbox Drafts {
    special_use = \Drafts
  }
  mailbox Junk {
    special_use = \Junk
  }
  mailbox Sent {
    special_use = \Sent
  }
  mailbox "Sent Messages" {
    special_use = \Sent
  }
  mailbox Trash {
    special_use = \Trash
  }
  prefix = 
}
passdb {
  driver = pam
}
passdb {
  args = failure_show_msg=yes %s
  driver = pam
}
plugin {
  sieve = ~/.dovecot.sieve
  sieve_dir = ~/sieve
}
protocols = " imap lmtp"
ssl_cert = </etc/dovecot/dovecot.pem
ssl_key = </etc/dovecot/private/dovecot.pem
userdb {
  driver = passwd
}
userdb {
  args = mail
  driver = pam
}

Apr  6 21:57:29 drakeclasher su[2346]: pam_unix(su:session): session
opened for user mailtest by dictator(uid=0)
Apr  6 21:59:55 drakeclasher su[2346]: pam_unix(su:session): session
closed for user mailtest

dictator at drakeclasher:~$ groups mailtest
mailtest : Domain Users mail users