Well, we started moving websites from a network server/local system hosting into their own locked down user account. The way it should have been in the beginning. We ran into a problem where sites that were using the CDO.Message com object couldn't send e-mails. They were getting an error saying that SendUsing configuration error. This one:
Issue: Number=-2147220502(0x800403EA) App  Source=CDO.Message.1 Description= -2147220960[0x80040220] The "SendUsing" configuration value is invalid
Well, turns out you need to change some permissions on a few things, metabase file and the nodes in the metabase.
metabase.xml file in
c:\windows\system32\inetsrv needs to have
everyone read permissions.
Using metabase explorer, make sure everyone has read access at the top, then LM (should be inherit by default), SMTP, and 1. And restart IIS.
If that still doesn't work, you might want to try using the IIS manager and change the permissions on the SMTP service (right click->properties->permissions) then remove everyone (if its there) and add it back in. Then restart IIS.