Hi,
I'm a troubleshooter and interested. Are you aware of "what are errors in the emails?" which you indicated? Also, the users who are not receiving emails belong to any specific domain or is it for common type of users? (e.g. hotmail, gmail or yahoo).
It could be script issue OR server issue that has to be investigated. If it is script issue it will be fixed and if it is server issue, I will let you know after investigation.
Thanks,
- Zeeshan