Neat virtual SMTP server connection restriction trick

I was floored to hear about this, but maybe that just shows I need to get out more. Turns out that you can flip a metabase flag to get some additional control over SMTP relaying. By default, if you require authentication and list one or more allowed IP addresses, both of those restrictions apply. However, you can set the SMTPIPRestrictionFlag value to use the logical-OR of those two factors, so that you can relay if you authenticate or if you’re coming from an allowed IP address. Mad props to Konstantin Ryvkin for admitting to this and to Devin for blogging it.