Hi,
I recommend you to check the following:
1. If a "Single Sign-On" option is enabled in the system, the user activation and reset password emails are disabled automatically: https://docs.sisense.com/main/SisenseLinux/using-single-sign-on-to-access-sisense.htm
2. Check if other email reports could be sent successfully. If no, please follow this troubleshooting guide to narrow down the issue.
3. Review the galaxy.log on the server and check if there are any errors related to the mail sending process that might explain the issue.
If that doesn't help, please clarify your Sisense version, platform and provide the updates on the troubleshooting suggestions mentioned above. Alternatively, you can reach out to our Support team for a further investigation.
Hope this helps!
Best Regards, Lily