Super Send has two inboxes:

Just Replies

As the name implies, this one will just show messages from prospects who have replied. You can quickly go through them and respond or not without logging in to each email account. Once you reply or mark it as finished, it will disappear.

Full Mailbox

Sometimes you need a little more power.... Any email sender you attach to super send you can now come in the full mailbox, switch between mailboxes, read all your mail, mark it as read, and even reply. Pretty Sweet.

This is just pulling unread emails. If you're struggling to load some messages for Gmail, make sure to use the following mailbox:

[Gmail]/All Mail

Use the toggle in the bottom left to switch between email accounts. You're only ever looking at one email account at a time.

How to toggle between email accounts in the Full Mailbox