People spamming via my zimbra server

After a quick through of the top 50 sender, i find nothing irregular. But i find the following in var/log/mail.log.. What is uni-hannover.de? this is the only IP i see.

Jan 24 23:27:48 mail postfix/smtpd[10101]: connect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:27:48 mail postfix/smtpd[10101]: setting up TLS connection from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:27:48 mail postfix/smtpd[10101]: SSL_accept error from tls-research6.dcsec.uni-hannover.de[130.75.16.49]: -1
Jan 24 23:27:48 mail postfix/smtpd[10101]: lost connection after CONNECT from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:27:48 mail postfix/smtpd[10101]: disconnect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:28:03 mail zmmailboxdmgr[10334]: status requested
Jan 24 23:28:03 mail zmmailboxdmgr[10334]: status OK
Jan 24 23:28:28 mail zmmailboxdmgr[10546]: status requested
Jan 24 23:28:28 mail zmmailboxdmgr[10546]: status OK
Jan 24 23:28:28 mail zmmailboxdmgr[10554]: status requested
Jan 24 23:28:28 mail zmmailboxdmgr[10554]: status OK
Jan 24 23:29:24 mail postfix/smtpd[10101]: connect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:24 mail postfix/smtpd[10101]: setting up TLS connection from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:24 mail postfix/smtpd[10101]: Anonymous TLS connection established from tls-research6.dcsec.uni-hannover.de[130.75.16.49]: TLSv1 with cipher DHE-RSA-AES25$
Jan 24 23:29:24 mail postfix/smtpd[10702]: connect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:24 mail postfix/smtpd[10702]: setting up TLS connection from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:24 mail postfix/smtpd[10101]: lost connection after CONNECT from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:24 mail postfix/smtpd[10101]: disconnect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:25 mail postfix/smtpd[10702]: Anonymous TLS connection established from tls-research6.dcsec.uni-hannover.de[130.75.16.49]: TLSv1 with cipher DHE-RSA-AES25$
Jan 24 23:29:25 mail postfix/smtpd[10101]: connect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:25 mail postfix/smtpd[10101]: setting up TLS connection from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:25 mail postfix/smtpd[10101]: Anonymous TLS connection established from tls-research6.dcsec.uni-hannover.de[130.75.16.49]: TLSv1 with cipher DHE-RSA-AES25$
Jan 24 23:29:25 mail postfix/smtpd[10703]: connect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:25 mail postfix/smtpd[10703]: setting up TLS connection from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:25 mail postfix/smtpd[10702]: lost connection after CONNECT from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:25 mail postfix/smtpd[10702]: disconnect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:25 mail postfix/smtpd[10702]: connect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:25 mail postfix/smtpd[10702]: setting up TLS connection from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:25 mail postfix/smtpd[10101]: lost connection after CONNECT from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:25 mail postfix/smtpd[10101]: disconnect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:25 mail postfix/smtpd[10101]: connect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:25 mail postfix/smtpd[10101]: setting up TLS connection from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:25 mail postfix/smtpd[10702]: Anonymous TLS connection established from tls-research6.dcsec.uni-hannover.de[130.75.16.49]: TLSv1 with cipher DHE-RSA-AES25$
Jan 24 23:29:25 mail postfix/smtpd[10703]: Anonymous TLS connection established from tls-research6.dcsec.uni-hannover.de[130.75.16.49]: TLSv1 with cipher DHE-RSA-AES25$

Jan 24 23:29:26 mail postfix/smtpd[10704]: Anonymous TLS connection established from tls-research6.dcsec.uni-hannover.de[130.75.16.49]: TLSv1 with cipher DHE-RSA-AES25$
Jan 24 23:29:26 mail postfix/smtpd[10702]: lost connection after CONNECT from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:26 mail postfix/smtpd[10702]: disconnect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:26 mail postfix/smtpd[10703]: connect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:26 mail postfix/smtpd[10703]: setting up TLS connection from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:26 mail postfix/smtpd[10702]: connect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:26 mail postfix/smtpd[10702]: setting up TLS connection from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:26 mail postfix/smtpd[10703]: Anonymous TLS connection established from tls-research6.dcsec.uni-hannover.de[130.75.16.49]: TLSv1 with cipher DHE-RSA-AES25$
Jan 24 23:29:26 mail postfix/smtpd[10101]: lost connection after CONNECT from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:26 mail postfix/smtpd[10101]: disconnect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:26 mail postfix/smtpd[10704]: lost connection after CONNECT from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:26 mail postfix/smtpd[10704]: disconnect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:26 mail postfix/smtpd[10702]: Anonymous TLS connection established from tls-research6.dcsec.uni-hannover.de[130.75.16.49]: TLSv1 with cipher DHE-RSA-AES25$
Jan 24 23:29:26 mail postfix/smtpd[10101]: connect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:26 mail postfix/smtpd[10101]: setting up TLS connection from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:27 mail postfix/smtpd[10704]: connect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:27 mail postfix/smtpd[10704]: setting up TLS connection from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:27 mail postfix/smtpd[10702]: lost connection after CONNECT from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:27 mail postfix/smtpd[10702]: disconnect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:27 mail postfix/smtpd[10101]: Anonymous TLS connection established from tls-research6.dcsec.uni-hannover.de[130.75.16.49]: TLSv1 with cipher DHE-RSA-AES25$
Jan 24 23:29:27 mail postfix/smtpd[10704]: Anonymous TLS connection established from tls-research6.dcsec.uni-hannover.de[130.75.16.49]: TLSv1 with cipher DHE-RSA-AES25$
Jan 24 23:29:27 mail postfix/smtpd[10702]: connect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:27 mail postfix/smtpd[10702]: setting up TLS connection from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:27 mail postfix/smtpd[10703]: lost connection after CONNECT from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:27 mail postfix/smtpd[10703]: disconnect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:27 mail postfix/smtpd[10702]: Anonymous TLS connection established from tls-research6.dcsec.uni-hannover.de[130.75.16.49]: TLSv1 with cipher DHE-RSA-AES25$
Jan 24 23:29:27 mail postfix/smtpd[10702]: lost connection after CONNECT from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:27 mail postfix/smtpd[10702]: disconnect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:27 mail postfix/smtpd[10101]: lost connection after CONNECT from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:27 mail postfix/smtpd[10101]: disconnect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:28 mail postfix/smtpd[10704]: lost connection after CONNECT from tls-research6.dcsec.uni-hannover.de[130.75.16.49]
Jan 24 23:29:28 mail postfix/smtpd[10704]: disconnect from tls-research6.dcsec.uni-hannover.de[130.75.16.49]