my mdaemon email server sending out spam

I have Mdaemon 6.0.6 installed on my windows machine and have done for nearly a year now without any problems - until now that is. It looks like a spam bot has got into my Mdaemon email server and is sending out lots of e-mails using my e-mail address and i need to stop it without me having to delete my email address. Trouble is I have no idea what to do. This is a typical log from a sent email not by me

Thu 2003-01-09 21:40:19: [208:3919] Accepting SMTP connection from [212.7.136.119]
Thu 2003-01-09 21:40:19: [208:3919] Looking up PTR record for 212.7.136.119 (119.136.7.212.IN-ADDR.ARPA)
Thu 2003-01-09 21:40:28: [208:3919] 10 second wait for DNS response exceeded
Thu 2003-01-09 21:40:28: [208:3919] 220 mydomain.com ESMTP MDaemon 6.0.6a; Thu, 09 Jan 2003 21:40:28 +0000
Thu 2003-01-09 21:40:29: [208:3919] HELO Akoky
Thu 2003-01-09 21:40:29: [208:3919] Spam Blocker checking 212.7.136.119 using 119.136.7.212.or.orbl.org...
Thu 2003-01-09 21:40:29: [208:3919] Spam Blocker A-record resolution of [119.136.7.212.or.orbl.org] in progress (DNS Server: 194.168.8.100)...
Thu 2003-01-09 21:40:39: [208:3919] Spam Blocker 10 second wait for DNS response exceeded
Thu 2003-01-09 21:40:39: [208:3919] Spam Blocker checking 212.7.136.119 using 119.136.7.212.relays.ordb.org...
Thu 2003-01-09 21:40:39: [208:3919] Spam Blocker A-record resolution of [119.136.7.212.relays.ordb.org] in progress (DNS Server: 194.168.8.100)...
Thu 2003-01-09 21:40:49: [208:3919] Spam Blocker 10 second wait for DNS response exceeded
Thu 2003-01-09 21:40:49: [208:3919] Spam Blocker checking 212.7.136.119 using 119.136.7.212.relays.osirusoft.com...
Thu 2003-01-09 21:40:49: [208:3919] Spam Blocker A-record resolution of [119.136.7.212.relays.osirusoft.com] in progress (DNS Server: 194.168.8.100)...
Thu 2003-01-09 21:41:00: [208:3919] Spam Blocker 10 second wait for DNS response exceeded
Thu 2003-01-09 21:41:00: [208:3919] Performing reverse lookup on Akoky (looking for 212.7.136.119)
Thu 2003-01-09 21:41:10: [208:3919] 10 second wait for DNS response exceeded
Thu 2003-01-09 21:41:20: [208:3919] 10 second wait for DNS response exceeded
Thu 2003-01-09 21:41:20: [208:3919] 250 mydomain.com Hello Akoky (may be forged), pleased to meet you
Thu 2003-01-09 21:41:21: [208:3919] MAIL FROM: <me@mydomain.com >
Thu 2003-01-09 21:41:21: [208:3919] Performing reverse lookup on mydomain.com (looking for 212.7.136.119)
Thu 2003-01-09 21:41:31: [208:3919] 10 second wait for DNS response exceeded
Thu 2003-01-09 21:41:41: [208:3919] 10 second wait for DNS response exceeded
Thu 2003-01-09 21:41:41: [208:3919] 250 <me@mydomain.com>, Sender ok
Thu 2003-01-09 21:41:43: [208:3919] RCPT TO:<remi@via.ecp.fr>
Thu 2003-01-09 21:41:43: [208:3919] 530 Authentication required
Thu 2003-01-09 21:41:43: [208:3919] QUIT
Thu 2003-01-09 21:41:43: [208:3919] 221 See ya in cyberspace
Thu 2003-01-09 21:41:43: [208:3919] SMTP session successful, 78 bytes transferred.
Thu 2003-01-09 21:41:43: ----------

I've obviously replaced my real domain name and e-mail addy with mydomain.com

I have blocked the following ip address which is listed in the log 212.7.136.119 but it's still sending out spam. i've now shut down the server til i can solve the problem. Any help would be much appreciated. Thanks