Constituent lists cannot be filtered based on the presence of an active email address. Thus, a list with over 50,000 constituents cannot be used for an email distribution even though fewer than 50,000 have an active email address. The end result is that the constituent list needs to be based on a static query created in the database view, and then that list needs to be refreshed each time an email is sent.
RENXT-I-6222
as well as a few Ideas that mention wanting to filter by the "Marked as: Requests no email" flag
The point being that to make best use of email marketing and for fundraisers to be able to plan their workflows, Lists work better if we can separate out to see how many can be efficiently emailed versus phone appeals versus need to be mailed.
related to RENXT-I-6727
related to RENXT-I-3475
related to RENXT-I-6962
related to RENXT-I-2661
Also, when using a workflow to add an action after an email is sent, it adds the action to all of the records who do not have an email address.