It's available for Windows. I use it every day - mostly on OS/2, but also on Windows, and I have several clients who have used it on Windows since the days when eMail infections became rampant.
The thing I like best about PMMail is the ease and clarity with which you can maintain completely separate email accounts. I run one instance of PMMail for support and it has accounts for 17 client mailboxes. I run another instance for my own 13 mailboxes (at several hosting services).