Estimates. Does the Estimate email sent by PrintJobManager use the "From" email address of the user who created the estimate?

Yes. You can also setup a general email as well that all emails would be sent from. (Sales@mine.com, Customer Service@mine.com, etc.) This would be set up in the General Settings area.

 

In general, the various email templates used by PrintJobManager are editable by you. The default subject line and body content can be edited by you to better tailor them to your company. And to save you time, the emails make extensive use of automatic merge fields for things like your company name, address, order number, order details, the print buyers details, etc.