Which file has the SMTP configurations/settings?

Hi

What is the file that normally has the SMTP config settings? I have an api account name from sendgrid however that doesnt work because it expects a domain with it. so I was thinking of directly modifying the file where this SMTP configurations live under program file\rhinosoft\serv-u but Im not sure what that file is.

I looked around for a .config and the only thing i found is .cnf however that didnt contain the settings.