Send email via your Gmail or Google Apps account

...from ISPs that don't allow port 25 traffic
...or from devices that don't allow authenticated SMTP

Install SMTP service (for XP, 2000, 2003, or 2008)
In IIS 6 manager
  Right-click the SMTP Virtual Server, Properties
Access tab
  Relay button
    Only the list below
      specify the IPs that may send email, including at least the IP of this server
Delivery tab
  Outbound security button
    Select Basic Authentication
      specify [username]@gmail.com (or Google Apps account @ your domain)
      and password
      Check: TLS encryption
  Outbound connections button
    TCP port: 587
  Advanced button
    Smart host: smtp.gmail.com

  - or -

Install hMailServer (for Windows 2000 through 2008)
Settings > Protocols > SMTP > Delivery of e-mail tab...
  Local host name: hmailserver.example.com
  Remote host name: smtp.gmail.com
  Remote TCP/IP port: 465
  Server requires authentication: Check
  User name: [username]@gmail.com (or Google Apps account @ your domain)
  Password: (yours)
  Use SSL: Check
Save
Settings > Advanced > IP Ranges > Add...
  Name: insideLAN
  Priority: 20
  Lower IP/Upper IP: (the range of LAN IPs that will need to send mail)
  Other...
    Anti-Spam: Not Checked
    Anti-Virus: Not Checked
  Require SMTP Authentication...
    Local to local e-mail addresses: Not Checked
    Local to external e-mail addresses: Not Checked
    External to local e-mail addresses: Not Checked
    External to external e-mail addresses: Not Checked
Save

With either method
Allow port 25 inbound to this server/disable McAfee rule which prevents it.
Configure your device/application to send email to the IP of this SMTP server.