Subscribe by Email plugin not functioning

We have a multi-site installation and currently one of our blogs is using this plugin. There are 54 subscribers listed in the subscribers list. The author has made one post and according to the plugin it was sent to 43 recipients, but when she asked her subscribers (her school faculty members) who did not receive the email notification, no one received them. They weren’t going to the spam folder either.

The contents page appears to set up correctly with “Posts will be included in the digests” being checked, including “All” categories .

I changed the notification from email from no-reply@*** to the author’s email address, thinking that might be causing an issue. I then went into the mail template and attempted to send myself a test mail, to no avail. It isn’t working.

We have the multisite privacy plugin installed and she used it limit access to her site by password only. Could this be affecting the subscriptions plugin?

Thank you in advance,

Caroline