To read emails from a mailbox, SliQ Submitter uses a standard protocol called POP3.
By default, if a POP client like SliQ reads emails, Gmail does not mark the email as read. However, you can change the settings to make Gmail show the emails as read as follows:-
1. Log into Gmail then access settings via the drop down menu on the config button at the top right, just under your account name.
2. Then click on the Forwarding and POP/ IMAP tab.
3. About half way down the tab, there is an option called "When messages are accessed with POP".
4. Change the setting to Mark Gmail's copy as read.
Now when SliQ reads/ downloads emails (and you haven't configured SliQ to delete the emails) then Gmail will mark the mails as read so you know which ones SliQ has processed.