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 System.Net.Mail.MailMessage 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.