I tried with both an email that wasn’t connected (my personal gmail account) and with the gmail account that controls the forwarded email address. My personal account receives all 3 tests okay. The one linked to the sender address receives only 1-2.
But my personal account still isn’t getting the subscription confirmation emails when I test subscribe.
I tried to subscribe an I did not received emails. You should ask the provider about that because is not good. Ask them is they have limits on the number of email you blog can send, or if you need to use an SMTP (ask them the SMTP parameters as well).
I checked out my domain provider’s info about SMTP settings and changed my gmail “additional account” SMTP settings and added that SMTP info to the Configuration section of the plugin and that fixed it.