You had better use Gmail, not Yahoo or Hotmail.
1. Please make sure DVR or NVR has connected to router and Internet successfully. You can judge by the picture below.
2. Please enable alarm and email alerts function.
3. Please log in your Gmail account.
4. Please open website below
5. Please tick turn on.
6. Please set up email in DVR setting like the picture below. If the mail test succeeds, it is working.
The SMTP server is smtp.gmail.com
port is 465
password is your Gmail account password
the sender is your Gmail account
the receiver can be any email.
Click Test. If the test succeeds, all is working.