How can I send e-mails from my ASP.NET Core web service using public free e-mail providers?

Question

I created a web service that's supposed to dispatch e-mails using a public free e-mail provider, e.g. GMail or Outlook.com

A few years ago, this would have been a snap using SMTP and STARTTLS. Yet, as of the end of May, 2022, Google and Microsoft no longer allow enabling "Less secure apps". So, I'm not able to use Basic authentication (i.e. user name and password) for sending e-mails using SMTP.

I have been searching for documentation on how to do things now, but I'm not able to succeed.

So, I asked the MailKit team, followed their suggestions at https://github.com/jstedfast/MailKit/issues/1620, but to no avail: https://stackoverflow.com/questions/76871274/how-can-i-send-e-mails-from-my-gmail-account-using-rest-service

Now I'm lost: How do I send e-mails from an unattended ASP.NET Core web service, installed in a Docker container, using a public free e-mail provider? What's an up-to-date, bullet-proof approach and solution?

Your answers are very much appreciated.

Answer 1

Most modern email systems use oauth authentication. The default flow requires a browser, for application access you typically a client secret to get the access token. The mail service will have admin support to create the secret. For gmail

https://support.google.com/cloud/answer/6158849?hl=en#:~:text=Go%20to%20the%20Google%20Cloud%20Platform%20Console%20Credentials%20page.,to%20add%20a%20new%20secret.

then use mailkit oauth support.

Answer 2

Thanks for trying to help!

I tried all the documentation provided so far, but to no avail. All I get is error messages and a browser window displayed for logging in. Documentation isn't helpful at all.

So, I give up now. This is too much rocket science for me. I will use a simple SMTP provider with basic authentication for my purposes.