Add incoming mail test item on admin dashboard

[hiifong]

Feature Description

Because incoming mail depends on plus addressing, if the mail provider does not support plus addressing, then incoming mail will not work. If the administrator is not aware of this, then they will waste a lot of time troubleshooting the problem. So I think we need to add this feature.

We can add a simple test by sending a test email to the REPLY_TO_ADDRESS address of the incoming mail. If the email can be received, it means that the current mail supports plus addressing.

If you have better ideas, you are welcome to leave your thoughts.

Screenshots

No response

[wxiaoguang]

Test for what purpose and how to really "test"?

[hiifong]

Test for what purpose and how to really "test"?

@wxiaoguang Updated description