Smtp server recomendation

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http://serverfault.com – I have a documentation program that needs to send mails to users. In order to do this it needs to use an smtp server. We have access to our internet providers smtp server. However that server requires password authentication. The documentation system does not have the ability to use this as there is no way for it to provide the password. Can I install an smtp server on my computer that does not require the authentication to send mail and then in turn can provide the authentication to the smtp server? And if I can install an smtp server on my computer what one is the best and free. I am on an (HowTos)