The classic ASP error "cdo.message.1 error 80040220 The "SendUsing" configuration value is invalid" is an error message indicating your ASP script (website) can't send its email out, or the IIS SMTP service is wrongly configured. Here is how to fix the latter issue.
Sometimes customers report their ASP mail script returning an error:
CDO.Message.1 error ‘80040220’
The "SendUsing" configuration value is invalid.
A quick Google search let me to realityme.net, where Doug explains the error is caused because the IIS_WPG user group doesn't have READ permission on the IIS SMTP service (SmtpSvc). This is easily resolved using MetaAcl.vbs.
Add READ permission for IIS_WPG to SmtpSvc
In order to resolve the "The "SendUsing" configuration value is invalid." error you have to use MetaAcl.vbs to add READ permission to IIS SmtpSvc server for IIS_WPG user group. On Windows Server 2003, if you don’t specify the default smtp server, it needs to obtain that from the IIS metabase. That isn’t allowed by default in IIS6, but you can add it with metaacl.vbs.
cscript.exe Metaacl.vbs IIS://localhost/SMTPSVC/1 IIS_WPG RUE
Here you can find & download the old Metaacl.vbs, just rename Metaacls.vbs.txt to Metaacl.vbs. If you prefer to use the graphical user interface (GUI), then start Internet Information Services (IIS) 6.0 Manager, or open it up in Computer Management (Computer Management -> Services and Applications -> Internet Information Services (IIS) Manager -> Default SMTP Virtual Server -> Properties -> Security -> Add). Add IIS_WPG and
And don't forget to do the same with Metabase Explorer, available in the IIS 6 Resource Kit, Google for "iis60rkt.exe" (local mirror). The path is Metabase Explorer -> SmtpSvc Permissons -> Add. I lost the screenshot over the years, sorry.
If this doesn't fix the error, you may need to reconfigure the CDOSYS object to use SMTP authentication and / or different SMTP server. Then you can send mail from ASP using CDOSYS.