I tried using the form on your site, and it seems to be working properly. I subscribed to your blog, and you can now see my email address in your subscriber list.
It’s worth noting that confirmation emails are only sent once, so if you previously attempted to subscribe but never clicked on the link in the confirmation email, you won’t receive a new email if you use the subscription form again today.
You can confirm your pending subscription here:
https://subscribe.wordpress.com/
If you’d like, you can send me an email via this contact form and mention this thread, as well as a few examples of the email addresses that didn’t receive a confirmation email. I’ll be happy to take a look at our email logs to find out what happened.