My Mail Server Server is Sendmail with MailScanner and F-Prot funtion to scan the mail. "dad" and "B321654" both are the users at the server. They can login and sent out the mail without any problem.
Only "dad" can receive mail.
But "B321654" can not receive mail ether from local nor others ISP, also without any rejected return-mail. ( but "dad" can do. )

Here below is the mail-log :-

/var/log/maillog

Mar 28 09:42:30 pluto sendmail[858]: h2S1gOO4000858: from=<frow@hknetmail.com>, size=798, class=0, nrcpts=1, msgid=<1048815536.3e83a7b01bea2@www.hknetmail.com>, proto=SMTP, daemon=MTA, relay=nweb.hknetmail.com [202.67.240.32]
Mar 28 09:42:31 pluto MailScanner[830]: New Batch: Scanning 1 messages, 1267 bytes
Mar 28 09:42:32 pluto MailScanner[830]: Virus and Content Scanning: Starting
Mar 28 09:42:34 pluto MailScanner[830]: Uninfected: Delivered 1 messages
Mar 28 09:42:36 pluto sendmail[886]: h2S1gOO4000858: to=<dad@typs.edu.hk>, delay=00:00:06, xdelay=00:00:01, mailer=local, pri=120670, dsn=2.0.0, stat=Sent
Mar 28 09:47:18 pluto sendmail[1009]: h2S1lIO4001009: <B321654@typs.edu.hk>... User unknown
Mar 28 09:47:18 pluto sendmail[1009]: h2S1lIO4001009: from=<frow@hknetmail.com>, size=0, class=0, nrcpts=0, proto=SMTP, daemon=MTA, relay=nweb.hknetmail.com [202.67.240.32]

Can you help or any idea ???

Thanks.