Thunderbird rewrite: integrate these essential Features (currently Addons)

[xUxSxExR]

If Thunderbird gets rewritten I can imagine at least for some time most addons will not work anymore.

I am sure a mailprogram doesnt need to be an entire browser, but changing its foundation, while Addons are already pretty few, could strip many of its needed features

• DKIM verifier: this is essential and should always be integrated. It works on nearly all mailservers. No reason not to integrate it by default
• Some carddav support for syncing contacts with Android. K9mail works perfectly like that, Thunderbird should allow syncing from a local .vcf file too
• Reply with Subadress: essential when using aliases and not wanting to accidentally use the wrong alias on a mail
• Thunderbird conversations: This will hopefully be completely integrated, not only showing received but also sent messages. Mails are used like Chat very often, and not having threads is horrible.
• Simple Template, mail templates. Mail programs like outlook for sure support this. Mails always look the same, especially if you are writing from a business with complex templates. Having this in TB is essential
• Send Later: This addon is very broken but solves an important feature currently standing out from Mailspring.
• Check if recipient viewed mail content: I dont know if this is possible without servers and loaded images, but any form to integrate this would be really helpful. Also a feature of mailspring.

Thunderbird is the best Mail client on the Desktop! But it needs to tidy up, fix its horrible UI, get modern and integrate essential features.

[pulse]

These all look like great suggestions. Specifically for the threaded conversation view (like the Thunderbird Conversations add-on but integrated into Thunderbird by default), there is another idea here: https://connect.mozilla.org/t5/ideas/true-threaded-conversations-in-thunderbird/idi-p/29558