XF 1.5 New users not receiving email confirmation


New member
Here is what used to happen when a new user would join our forums:
1. They sign up
2. They get an email to click on the link to confirm their signing up.
3. I get an indication that they signed up and am asked to approve them.
4. I approve them or reject them.
5. If they are approved they get a confirmation email with an intro to the forums.

Here is what is happening now and has been for the past couple of months:
1. They sign up
2. They get no email to confirm.
3. I do not get any indication on my end of the site that someone has joined the forum unless it's a spam account.
4. I have no way to approve the members who are non-spam accounts other than to look them up via the admin panel
5. They do not get a confirmation email from the forums with an introduction (which is important to us) when I do approve them from the admin panel. This is when I am marking them from the status of "Awaiting email confirmation" to "Valid"

I see in my server error log that the emails are not getting sent. I have no add-ons on the site that could be interfering.
Any advice would be appreciated. I have been going around in circles trying to get this resolved.