C# class to Email message + attachment - must include intregation testing to an email account

The email account is arbitrary (gmail, gmx, hotmail, outlook etc.) - ideally free but not necessarily so. The final class will be called silently from a host application logging trace details and sending via email. As you may well know the actual email code using [login to view URL] is trivial. All the work is in the credentials fitting with the provider. Find me a free or low cost email provider, a C# class with a testing harness (console app is fine or simple windows form app that allows for repeated emails up to some max with defined text and attachment file) that works repeatedly. - that's the job. Frequency is low (3-5 emails by 100 users within a 30min period). Successful test is running 2 instances of test harness and firing 1 email per 30 seconds for 10 minutes simutaneously with a 10k attachment and a 1k text body. If the emails all show up on the email client without issues it's a success. Email service must support up to 1 month worth of logs: 5*100*30=15000 emails max per month before they are deleted.