hMailServer is a good and free e-mail server for Windows. You can also integrate it with SpamAssassin to identify spam.
- Download SpamAssassin for Windows from Jam Software here
- Download NSSM here and save it in c:\Windows. Then type "nssm install SpamAssassin” in a console
- Select "spamd.exe" in SpamAssassin installation folder as application.
- Put these parameters in options field: -l -s spamd.log --round-robin
- Go to services control panel and start SpamAssassin
- Set options in hMailServer to use SpamAssassin
- Set up a new scheduled task to run sa-update.bat to automate the process of downloading and installing new rules and configuration