How does reply detection work?

Every hour, Quickmail automatically scans your gmail inbox for replies and bounce notifications. 
So it's normal that sometimes you'll catch replies/bounces before Quickmail does.
Just make sure to keep the replies and bounces in your inbox for at least a day so that Quickmail has ample time to detect them.
Archiving the responses or putting them in labels/folders is also fine - as long as they are not deleted or moved to the spam folder.

If a reply or bounce is detected, Quickmail will automatically tag the associated prospect as "Responded" or "Bounced" and follow-ups will be cancelled automatically.

Green conversation icon = Responded
Red conversation icon = Bounced

You can view the prospect to see more details. More information about prospect status here -> Prospect Status

Archiving and labeling emails is also fine, just make sure to use only alphanumeric characters in your gmail labels (don't use parentheses and slashes).

If you want to initiate the inbox scan immediately, you can go to Settings -> Inboxes -> email settings -> click "Check replies now"

Note: Bounced prospects will also get marked as "bad" so they will no longer be able to start a new sequence (even if you accidentally reset them). 

You can view the bounced prospect and update the email address to remove the "bad" label.