There are a couple of relatively nice mail options for macOS that include Canary (limited tracking), Spark (send later), Mailbutler (tracking, send later, etc.) - but Canary and Spark have various glitches that have ultimately caused me problems in the way of composing messages and not having everything together. MailButler is simply too expensive.
Are there any open source tools with accompanying services that we can use in place of Mailbutler to accomplish its goals? The following functionality are services I'd like to see in such a solution that is integrated into Mail.app:
- Usage on unlimited email accounts
- Send Later
- Open / Link / Details tracking
SendLater was nice and used to exist, but appears to have been developed by Mailbutler's developer and then discontinued (SE suggestion, led to http://www.chungwasoft.com/sendlater/ which redirects to https://www.mailbutler.io//sendlater - now gives 401 error). Notwithstanding even this was not enough since tracking would also be exceptionally useful.