While reprint ing invoices we keep getting a "mail not sent" error message. When we tried reinstalling, after erasing the ists and isnz folders and recreating them with some blank text files in them,  there was the old configuration data still in the fields for Tas-c (configuration, email setup) ... like the the program was pulling configuration data from the server or like  we had not erased the config files.

The "email was not sent" message is definitely related to making the connection to the SMTP server.  
 
I had one customer yesterday using Exchange Server and he had installed an SP from Microsoft that disabled relay so he had to manually enable it for the IP addresses of the local workstations before they could email from Evo.