Can anyone share some tracking methods or process they have so 1. they know where their source of traffic is coming from (email, banner, paid ads, referrals, ?)? 2. they can link down to the granular level and id an email?
Google Analytics, Mixpanel or Kissmetrics are good tools that allow you to do it. The only inconvenient thing about the last 2 is that you need to set up "events" to understand your flow it and it might just take too much time.
If you've configured your ecommerce module on GA you will probably receive this data now and can sort with a good level of detail when a conversion/transaction happens and where it came from. Banner Ads when run on Google Adwords are easily tracked by your GA account. Email is a little bit trickier because it requires that every single link within your email comes with a campaign tracker, but that also can be built on a fly with Google Url builder https://support.google.com/analytics/answer/1033867?hl=en
Let me know if you want to expand on the subject :)
If URL campaigns are not an option then you might need to set up "event" on GA to track something like a referral.
The tracking KPIs that must be your process:
1. Acquisitions tracking: If you want to know from where came your visits, Google Analytics is your tool. Is a session centric tracking, that it's really powerfull with some settings addeds.
Mixpanel and Kissmetric, both are really strong to understand who (name, email, sex, age, etc.) is doing what. It's required that your website use an register or loggin process. And need a lot of event settings to get acquisition information.
2. For granular info, a software like mailchimp can give you really strong information if it's setting well. But anyway if you use another tool, a tracking method that helps a lot it's the URL builder, here a chrome extension.
Hope this help you. And let me know if you need more information about this subject.