I'm having a similar problem so I searched and found this thread... My email setup is to have my hosting service (Dreamhost) SMTP send email. (I tried the PHP setup and got some sporadic responses for "followed" content but none of the "contact us" links would send any mail. I've checked the logs and they show no failures and checking the dreamhost account there are no returns/unables. But (1) Tetst email works from ACP and "Contact Us" solidly works.
First... are you still following the content you are wanting to get notifications for?
Double checked for followed content and checked with other users and they are not getting followed emails either.
If so... have you checked to make sure your see if your settings are still configured to notify you via email? (Click on the bell and then "Notification Settings".)
Still set to "A notification when new content is posted" --->Email
If those are all working... are you receiving ANY email from your site? Test by going to ACP > System > Settings > Email Settings > Test Settings
Received test email OK
If you are not getting the test email, it means IPB has sent the mail, but your outbound mail server was not able to deliver it to you. Should that be the case, it may be a SPF/DKIM setup issue.
But let's start with those and see how far we get. 🙂
I have to think its just a notification/email setting since the other emails (test/contact) are going out ok... but I don't know the code.
Any help appreciated