[Dovecot] How to turn off "plus" delivery

[gene]

I use a lot of plus-style addresses (me+stuff at example.com), except I use underscore as the separator rather than plus (me_stuff at example.com).  My mail logs are full of messages where dovecot looks for a mailbox named "stuff", fails, then delivers to my inbox.  Is there a way to turn that off so that dovecot automatically delivers to my inbox?

Thanks!

Here are the details:

 > dovecot --version
1.2.15

 > dovecot -n
# 1.2.15: /etc/dovecot/dovecot.conf
# OS: Linux 2.6.38-8-server x86_64 Ubuntu 11.04 
info_log_path: /dev/null
log_timestamp: %Y-%m-%d %H:%M:%S 
ssl_cert_file: /etc/ssl/server.crt
ssl_key_file: /etc/ssl/server.key
ssl_cipher_list: ALL:!LOW:!SSLv2:ALL:!aNULL:!ADH:!eNULL:!EXP:RC4+RSA:+HIGH:+MEDIUM
login_dir: /var/run/dovecot/login
login_executable: /usr/lib/dovecot/imap-login
mail_privileged_group: mail
mail_location: maildir:~/Maildir
mbox_write_locks: fcntl dotlock
imap_client_workarounds: outlook-idle delay-newmail
lda:
  postmaster_address: postmaster at xxxxxxxxx.com
  postmaster_address: postmaster at xxxxxxxxx.com
  mail_plugins: sieve
  quota_full_tempfail: yes
  deliver_log_format: msgid=%m: %$
  rejection_reason: Your message to <%t> was automatically rejected:%n%r
  postmaster_address: postmaster at xxxxxxxxx.com
  mail_plugins: sieve
  quota_full_tempfail: yes
  deliver_log_format: msgid=%m: %$
  rejection_reason: Your message to <%t> was automatically rejected:%n%r
auth default:
  mechanisms: plain login
  passdb:
    driver: pam
  userdb:
    driver: passwd
  socket:
    type: listen
    client:
      path: /var/spool/postfix/private/dovecot-auth
      mode: 432
      user: postfix
      group: postfix
plugin:
  sieve: ~/.dovecot.sieve
  sieve_dir: ~/sieve
  sieve: ~/.dovecot.sieve
  sieve_dir: ~/sieve


> cat ~/.dovecot.sieve
require ["regex","fileinto"];

if header :regex ["X-Bogosity"] ["^ *Spam,"] {
  fileinto "caughtspam";
  stop;
}


# excerpt from mail.log:
postfix/pipe[32255]: BE4FCE24069: to=<gene_att at xxxxxxxxxx.com>, relay=bogo_filter, delay=1.2, delays=0.13/0.01/0/1.1, dsn=2.0.0, status=sent (delivered via bogo_filter service)
postfix/qmgr[28916]: BE4FCE24069: removed
postfix/cleanup[32254]: DBA1EE2406E: message-id=<1310331364610.sdc.29057010.18396.155116668 at connect2.wireless.att-mail.com>
postfix/qmgr[28916]: DBA1EE2406E: from=<sdc.29057010.18396.155116668 at connect2.wireless.att-mail.com>, size=7859, nrcpt=1 (queue active)
dovecot: deliver(gene): sieve: msgid=<1310331364610.sdc.29057010.18396.155116668 at connect2.wireless.att-mail.com>: failed to store into mailbox 'att': Mailbox doesn't exist: att
dovecot: deliver(gene): sieve: script /home/gene/.dovecot.sieve failed with unsuccessful implicit keep
dovecot: deliver(gene): msgid=<1310331364610.sdc.29057010.18396.155116668 at connect2.wireless.att-mail.com>: save failed to att: Mailbox doesn't exist: att
dovecot: deliver(gene): msgid=<1310331364610.sdc.29057010.18396.155116668 at connect2.wireless.att-mail.com>: saved mail to INBOX
postfix/local[32261]: DBA1EE2406E: to=<gene_att at xxxxxxxxxx.com>, relay=local, delay=0.05, delays=0.01/0.01/0/0.03, dsn=2.0.0, status=sent (delivered to command: /usr/lib/dovecot/deliver -c /etc/dovecot/conf.d/01-dovecot-postfix.conf -n -m "${EXTENSION}")
postfix/qmgr[28916]: DBA1EE2406E: removed