Delay in sending mail

add: "-Rt0" to the 'server_args' on file: /etc/xinetd.d/smtp_psa just like :
server_args = -Rt0 /var/qmail/bin/relaylock.....


Then restart xinetd:
# /sbin/service xinetd restart
Under PLESK control panel, go to SERVER -> Services: MAIL
Check this:
Mail Names for POP3/IMAP accounts:
--> Only use of "compound" POP3/IMAP mail accounts names is allowed
(that will force you to use "mailname@domain.ext" as username on email-client's
"server configuration" when checking mail)