The messages are being held in qmail queue for 20-30 minutes without sending.
/usr/local/qmail/queue/lock/trigger has incorrect permissions and/or owner, e.g.:
# ls -lh /usr/local/qmail/queue/lock/trigger prw--w--w- 1 mailnames qmail 0 Aug 15 15:32 trigger
Change the owner of this file to qmails:qmail:
# chown qmails:qmail /usr/local/qmail/queue/lock/trigger
Please see LWQ for additional details.