I′ve the same problem in some cases. I′d like to explain the “some cases”

If the Email-address is filled in the first time, then an Confirmation-Email will be sent by the abonnement widget. If you confirm immediately, then it will except the new email-follower.

If a user unsubscribe and like to re-subscribe again, the widget says, that a message is sent, but it isn′t sent. I tried that with 3 different Email-addresses with the same problem.

I don′t know what happens, if you forget to click the confirmation or if you delete the confirmation message by accident? Is it possible to get another mail with the same email-address? I don′t think so.

A workaround is, to ask the user, to write a comment with his email-adress. Here he/she has also the possibility to subscribe. In this case the email will be sent.

For some reason, the abonnement plugin of Jetpack will store the email-address. Maybe for Anti-Spam-reasons? If yes, it′s done in a bad way.

Maybe it should be possible to fix this problem for people who like to re-subscribe the blog. Once the unsubscribe, the don′t get an confirmation-email anymore.

You′re welcome to try it at my site: https://www.van-der-voorden.com

Many greetings
René