[Dovecot] High level of pop3 popping causing server to become unresponsive

[Root Kev]

Currently cannot use IMAP as our application to access the mailbox
currently is only setup to access pop3 mailboxes.  We are currently using
Dovecot 2.1.4.  Below is the majority of our configs, it is mostly basic:

protocols = pop3
listen = ***Address here***
base_dir = /var/run/dovecot1/
instance_name = Popper
login_greeting = Popper
mail_location =
mbox:/var/empty:INBOX=/opt/mailstore/spool/mail/%u:INDEX=MEMORY

!include conf.d/*.conf
!include_try local.conf

disable_plaintext_auth = no
auth_mechanisms = plain
log_path = syslog
syslog_facility = mail
auth_verbose = yes
log_timestamp = "%b %d %H:%M:%S "
namespace inbox {
inbox = yes
}
mail_privileged_group = mail
lock_method = fcntl
mbox_read_locks = fcntl
mbox_write_locks = dotlock fcntl
pop3_uidl_format = %08Xu%08Xv
passdb {
  driver = checkpassword
  args = /usr/bin/checkpassword
}
userdb {
  driver = prefetch
}