Thanks for using ActivMail, this page should help you get started using it in your application.
ActivMail for ColdFusion Architecture
The core of ActivMail is a set of Java Classes that follow the SMTP RFC for sending email. The Java Classes are exposed to ColdFusion with the CFX_ActivMail Java CFX API Custom Tag.
The CFX_ActivMail tag is not typically called directly however. ActivMail comes with a ColdFusion custom tag called CF_Mail. CF_Mail works very similar to ColdFusion's own <CFMAIL> tag, and it is very easy to convert an existing CFMAIL to CF_Mail (often it only requires changing the tag name).
The CF_Mail tag has three child tags CF_MailAttachment, CF_MailHeader, and CF_MailParam. The CF_MailAttachment tag is used to send attachments in email, and has several attributes that allow you to customize how the attachment will be interpreted by the end user. The CF_MailHeader tag is used to add custom headers to the email message. The third child tag CF_MailParam does not introduce any new functionality, it exists simply for backwards compatibility with ColdFusion's built in <CFMAILPARAM> tag. We recommend that you use CF_MailAttachment and CF_MailHeader instead of the CF_MailParam tag.
ActivMail has the ability to send personalized email message directly utilizing a ColdFusion query. Using ActivMail you can pass the personalized messages of to multiple SMTP servers for sending. With ActivMail you can use as many SMTP servers as you want, with each server added the speed at which you send email increases. The architecture for this process is illustrated below.
ActivMail Documentation