Other Exchange server sending spam

[gadgethome]

Hi, Our IP address is coming up as blacklisted and when sending to some clients, emails are bouncing due to security policies. Added an spf record on the domain and also using a good reliable smtp provider called smtp2go. We are not using the standard smtp port 25.

Ran some online tools and one says it may be the "Cutwail" virus sending emails. Anyone come across this before? Any other recommendations to block spam going out on an Exchange server?

Thanks