About your new feature:
No sorry the mail api will show you the attachments if you click them, just like mails are only accessible if you open the inbox before.
I theory yes it is possible - Using the Mail ID you can get the attachments list synchronously (not waiting for an event). But I have had problems with this API in working on MailLooter. The API function GetAttachedItemInfo(...) seems to fail sporatically when called before a mail is read with RequestReadMail() / EVENT_MAIL_READABLE. I had to change MailLooter to get the attached info after reading the mail for it to work reliably.