E-mail server smtp e-mail hanging in the e-mail queue

Hi, I have thisla the problem when I want to send an e-mail via roundecube, which will be stuck under Start / Tools and Settings in the e-mail queue. I have installed the Plesk Premium Anti-Virus and the SpamAssassin. The SMTP server is postfix, and the IMAP / Pop3 server is Devecot. The log files which are located under / opt / psa / var / log / maillog spit me this out:

Nov 11 18:17:10 rs000553 postfix/smtpd[30697]: connect from ip-37-24-172-75.hsi14.unitymediagroup.de[37.24.172.75]
Nov...

E-mail server smtp e-mail hanging in the e-mail queue