Hi, I wanted to share with everyone my experience with these two plugins: Subscribe By Email and HTML Email Templates.
I had HTML Email Templates installed already, and was using Jetpack to automatically send emails to people who had subscribed to receive notice when a new blog post was published on our site. However, I wanted to be able to customize the notification emails, which is not possible in Jetpack. So I exported all our subscribers from Jetpack, installed Subscribe By Email, and imported all the subscriber email addresses. So far so good.
But then we published a blog post and I did not receive any email notification (I have myself on the list of subscribers).
I looked in SBE->Sent Emails, which told me that an emailed been sent to all subscribers. Then I tried resubscribing using the Follow button, which I had opted to display at the bottom of every page on the site. But I didn't receive a confirmation email for the subscription.
So I deactivated all my plugins except for SBE, and tried resubscribing again and it worked.
So then I went through one by one re-activating my other plugins, and HTML Email Templates was the culprit. That surprised me, since it's another WPMU DEV plugin...
Also, wanted to let people know that if you enter the same email address in the Follow box it won't resend a confirmation email if you're already subscribed. However, it will show you the "Thank you! A confirmation email is on the way..." dialog, even though (since you're already subscribed) no confirmation email is on its way. So I just kept on canceling my subscription in SBE->Subscribers and then resubscribing, while I was troubleshooting.
I hope this is helpful to anyone who is having trouble with SBE notification emails, and also that someone from WPMU can look into this conflict between plugins.