E-mail servers send e-mail by first looking up the MX (Mail eXchange) record for your domain name. You can have more than one MX record with different priorities.
Example:
MX 10 mail.mydomain.com
MX 20 mail2.mydomain.com
MX 100 backupmail.mydomain.com
In the case above, the mail server will send first to the machine mail.mydomain.com by looking up its "A Record" If it is unable to deliver e-mail, then it will try the one with the next priority which would be mail2.mydomain.com, and lastly the backupmail.mydomain.com will be tried.
If there are no MX records, the mail servers will use the "A Record" for the domain.
You want to make sure that all your MX records are going to Spam Sleuth Enterprise or to a store-and-forward backup server, which will relay the messages to Spam Sleuth Enterprise when it is available. If you left the IP address of your e-mail server the same, and gave Spam Sleuth Enterprise a new IP address, then you'll need to change your MX records to go to Spam Sleuth Enterprise.
To test your MX records in Windows:
NSLOOKUP
>SET TYPE=MX
>mydomain.com
[Lists the MX Records for mydomain.com]