Rated 4 out of 5 stars

yazan: dilbar tarih: Eki. 17, 2017 ·

If one mail failed (due to wrong email/else) during schedule process that stuck another last all mails in outbox....if anyone facing this issue please reply for solution.

This review is for a previous version of the add-on (6.3.1). 

yazan: Jonathan Kamens (Geliştirici) tarih: Eki. 17, 2017 ·

I agree that this is annoying.

Unfortunately, it's a Thunderbird bug, not a bug in Send Later. I reported it to the maintainers of Thunderbird almost six years ago: https://bug635044.bugzilla.mozilla.org/show_bug.cgi?id=749654 . Unfortunately, they still haven't fixed it.