I hope my discovery can help some of you on Zen-Cart 1.5.3 running on Window XP. To send mail out successfully, your Windows server has to have Visual C++ 2008 redistribution package installed, OpenSSL for Windows, and some config in php.ini and Apache bin directory.

1. Enable php_openssl.dll and sockets from php.ini if phpinfo only displays “tcp, udp,” in Registered Stream Socket Transports.
extension=php_openssl.dll
extension=php_sockets.dll

2. Make sure that the extension_dir points to my extension directory, not the default ./ location.
extension_dir = “c:/php53/ext”

3. Rename these 2 files so the same files are loaded from c:\php53 (This step is important if you see multiple ssleay32.dll in Apache & in PHP)
C:\Apache2\bin\ssleay32.dll => old-ssleay32.dll
C:\Apache2\bin\ssleay32.dll => old-libeay32.dll

If everything is OK your phpinfo(); you should ss these stream socket transports
Registered Stream Socket Transports: tcp, udp, ssl, sslv3, sslv2, tls
4. Now you can go to ZenCart Admin Email options and config all required parameters. Make sure Email From match your SMTP Email username. Port should be 587 or 465 depends on Secure Layer is required or not on your server. Either port will work on Windows machine.