Here is the work around how you can configure your seafile server installed in Microsoft Windows Operating System.
The configuration file in windows depends on where you installed your seafile program. I have installed seafile in Windows 10 in my C:\ drive. So my default location for seafile configration file seahub_settings.py is:
You can right click on the file and will see an option of "Edit with IDLE". If you don't see then open it with notepad.
Please add the following lines to seahub_settings.py to enable email sending.