Zombie junk: Deleted junk e-mails keep reappearing?

Hi Sandra Andina1,

As it seems you've isolated the behavior in question to a single email account, the next step would be to assess how that account is configured. For instance, if set up as a POP account, changes you make on the Mac would not be reflected at the server (i.e. the RNC website you describe) and the next time Mac Mail checks the server, it would redownload those messages.

The article Change Account Information settings in Mail on Mac covers how to make general changes to your account. Not every email provider supports IMAP (though most do), which would allow for changes made on the Mac to reflect at the server as described in the information shown in the "email accounts" link at the top:

"Email account types

You can use various types of email accounts in Mail. Some of the most widely used account types include the following:...

• IMAP accounts: Messages are stored on a mail server until you delete them. When your account connects to the server, it’s synced so that the messages on your Mac are the same as those on the server. Messages are accessible from different computers and locations where you use the account....
• POP accounts: Messages are stored on a mail server and are downloaded to your Mac when you access your account. The messages remain on the server until they’re deleted from the server."

Check with your email provider to verify the correct settings and options for configuring that email address in Mac Mail so that changes you make don't impact your ability to send and receive email through that address.

Regards.

Hey Sandra Andina1,

If you haven't already, try running Connection Doctor to see if there are any issues detected in the Mail app with your account: Use Connection Doctor in Mail on Mac - Apple Support

Cheers!