Create a lead assignment rule to send the email to the leads monthly?
Use an email execution vendor to send emails for marketing campaigns?
Use the standard salesforce mass email tool located on the leads tab?
Create an email alert workflow rule to send the email to the leads monthly?

Is it possible to make a callout from APEX to a SOAP web service that uses NTLM authentication? If so is there documentation and or samples?

 

I was able to generate an apex class from the WSDL but I don't know how to use it with NTLM auth and I have a funny feeling its not even possible.

 

NTLM authentication is always getting in my way (unless I'm building in .NET) but I have no say in what authentication protocol is used.