How to add a custom SMTP email provider?

Can you add a custom provider for email? I see their is a default list on the website but no details on how to add a custom one

you can use any SMTP

https://casdoor.org/docs/category/email/. I see 4 email providers (MailHog, Brevo, Azure, SendGrid) but no option to add any new SMTP

Went into the code and found that it does support a general SMTP provider. I can always add in a new pull requests for any custom providers. Seems simple enough ✅