The easiest way to send emails from FlutterFlow is to use ready-made solutions.

Statistical comparison of various email services. Such as Gmail vs Outlook, SendGrid vs Mailgun and a few others.

I think that you have an overestimated opinion about the vendors' SDK, not all of them have acceptable quality, but let's leave it to the discretion of the developers themselves. What is really important for our clients who use the EmailJS service from the back-end is flexibility and freedom of choice. If vendor "X" suddenly stops working for you or if there are any problems, the migration to another vendor will take several days. With the EmailJS service, about 10 minutes: add another service and move your traffic to it.

Indeed, someone could copy your code, but they will only be able to send your templates, with your content, and will not be able to send a custom email with their own content (spam). Which is absolutely not interesting for attackers.

This is a misconception.

EmailJS uses the "App Password", almost all email providers provide the option to generate it.

the EmailJS service is not a mail agent. It is not suitable for corporate correspondence; that is not its purpose. However, you can use the service to initiate the conversation.

Thanks for your feedback! In fact, there is no way we can prove to you that the content of the emails does not interest us. Over time, trust in our service will increase.