When the platform is OTHER and the Password Management is set to Manual for the managed account, this email "Manually Managed Account Password Requires Change" will be sent when the password requires changes.
This has been addressed in the 2.5.917 release of TPAM.
The line item from the 2.5.917 Release Notes from the "Resolved Issues" section:
"Manually managed account password change email notifications not being sent for all accounts on the system. BFER 8651"