Thanks Farhan - For your step #1, are you referring to "allow email router" as the "email router" option in the same dropdown where you can select to send user emails through "outlook crm client" or are you referring to a different "allow email router" option on the user page?
For your step #2, where/how does the user specify his credentials to allow the email router to send emails?
For your step #3, where does the user set "send as user" = true?