If you come across this ancient bit of code in a Classic ASP project.
CDO.Message.1 error ‘80040220’
The “SendUsing” configuration value is invalid.
It might not be what you think…
Go into IIS, Application Pools, find your website, Right Click and Advanced, then check this setting:
For me this was set to something else and caused this error. As soon as I changed it the error vanished.