Change Spammy Rules
This is a fairly decent plugin, especially for agencies. But, the threat of the MP team blocking my entire account because of client "17" doing some spammy crap is a HUGE deterrent. Why use this plugin if you've got the option to close my entire account? I wouldn't. If you would, please change this to be per website and not for the whole account. At least that would be something that we can deal with. Especially from an agency perspective.
Add the ability to initiate email messages and add/remove contacts from lists based on subscriber actions.
Design WordPress "System" Mails
Add a way to design all WP system emails in MailPoet - such as "Forgot Password", or "New User", etc.
Better Template Manager
a screen where you can see and manage all templates (without having to create a new email) the ability to save a template after making changes to it (instead of saving a new one every time) ability to 'favorite' a template and have it appear at the top of the 'choose your template' page ability to hide or remove other templates so users don't choose to make off-brand emails
Better segmentation options
Segmentation options are rather limited right now. Even a simple set of "I'm interested in" options for subscribers isn't possible. This could be significantly improved in two ways: add the option to segment based on wp_usermeta fields. This would allow me to gather subscriber information by many other methods (Gravity Forms, Buddy Press, etc), and then create email segments based on that. add a PHP API which would allow me to define my own segments by any criteria I want. While this would require a developer to take advantage of, it might make it easier for creating new segmentation options in MailPoet itself, so possibly worthwhile for both third party and your own developers :-)
Streamline Email Newsletter process
I just migrated from Mail Poet version 2 to version 3 and only did so because SendGrid is requiring it. Mail Poet version 2 is a lot more efficient and more streamlined with respect to sending newsletters. In version 2, the newsletter can be sent out with one click. Furthermore, the screen with newsletters (emails) in Version 3 is NOT as clean and user friendly as version 2. In Version 2, the templates were highlighted in light blue and allowed to easily distinguish between the templates and those sent.
Automatic Email to those who haven't bought or visited the website in x amount of days
Something like: We noticed you haven't shopped with us for a while. Check out our new products bla bla blah then SHOP button.
Better Source Code Mode
Some HTML tags gets overwritten when editing in "Source Code" mode. There are easy workaround for us to use RTL with MailPoet but it require direction tag which gets OVERWRITTEN whenever added.