I love SmartTask - and from my experience with SalesFlare, I miss this functionality, which makes the tool far more open, and stops me from jumping from app to app. (Salesflare does not do projects - so that is what I like in SmartTask. Not having the mail integration stops me from fully committing to use SmartTask)
Email integration (pop3, IMAP) connected with CRM - create new contacts, opportunities, email client functionality, Hooking up CRM contacts from the email function with the project.
Flowlu, like SalesFlare also has this type of integration (salesflare even looks for accounts on the web and enters the data in the CRM if that is the right one for you - and when an email comes from the same domain, offers to add that person to the account - pretty brilliant). It prevents a lot of manual entry work of contacts. Also, being able to add multiple email accounts, and being able to choose from which email you want to answer (same as sent to, or choose). Showing the email timeline from a contact.
This is different from sending an email to a contact or project which is currently possible. Trello has a similar function - and unless you store the convoluted email address somewhere in your mail client, it is impractical in my point of view. I have used Trello for many years - never could make that function work.
Hope this helps your decision-making.
Keep up the good work, guys!