How To Configure IIS SMTP Server To Forward Emails Using A Gmail Account (Smart Host)

This is very useful when you want to test your outgoing email for SharePoint but not have access to an SMTP server.

1. Create and setup a Gmail account to use POP3
• Enabling POP3 in Gmail: http://mail.google.com/support/bin/answer.py?answer=13273&cbid=wl8yzeug2lob&src=cb&lev=topic
2. Install the mail server role (POP3 and SMTP) 
3. Configure the IIS Server to forward messages using that account:
• IIS SMTP Virtual server -> Properties ->
• Access Tab

• Relay Button

• You can specify only the servers that you want to be able to send email here by selecting Only the list below and adding your servers IP addresses.
• Delivery Tab

• Outbound Security Button

• Select Basic Authentication and specify your Gmail account  and password. Check the TLS encryption. (If you use other SMTP server, it may not support TLS and cause error)
• Outbound connections button

• Set TCP port to 587 (This is Gmail port, default port should be 25)
• Advanced Button

• specify the smart host as smtp.gmail.com
• Now configure the Outbound email in SharePoint to send email to the server where you have installed this SMTP server.

Source: http://fmuntean.wordpress.com/2008/10/26/how-to-configure-iis-smtp-server-to-forward-emails-using-a-gmail-account/