[recursive]

SMTP4dev is a good option for Windows.

[lagadu]

Personally I use Papercut and so far I'm pretty happy.

[masklinn]

If you don't need the complexity of a full-blown visualisation UI, you can just (assuming you have Python on the machine) run

     python -m smtpd -n -c DebuggingServer localhost:1025

it will dump all mail to stdout.

(change port as you see fit, below 1024 requires root/sudoing)