How can I track click through rates and open rates?
In the current version (1.2) of Mail Campaigns you cannot track open rates and click through rates.
Mail Campaigns v2.0 will provide open, click, and unsubscribe rates by default.
I have a 20,000+ email list. Can this plugin handle that size of list?
v1.* cannot. Because it uses Mail Delivery Methods, Mail Campaigns
v2.0 will be able to.