Well, you didn't mention you want to keep receiving emails...
OK, here's solution for you:
*) Keep below SQL columns on table "vmail.mailbox" set to 0:
enablepop3
enablepop3secured
enableimap
enableimapsecured
enablesieve
enablesievesecured
It will disable POP3/POP3S/IMAP/IMAPS/Managesieve services for this user.
*) Keep below column on table "vmail.mailbox" set to 1:
enablesmtp
enablesmtpsecured
enabledeliver
It will allow Postfix to accept emails for this user, and allow Dovecot LDA to deliver accepted email to user mailbox.
NOTE: with enablesmtp=1 and enablesmtpsecured=1, this user is allowed to send email via SMTP/Submission.