Contacts with working email addresses appearing in bounce list?

Contacts with working email addresses appearing in bounce list?

Hi,

I am struggling to figure out why many of my contacts (for which I know I have working email addresses) are ending up in my 'Bounced Contacts' list in campaigns?

How do you remove contacts from this 'Bounced Contacts' list and add them back into the 'Active Contacts' list?

I am losing out on sending over 100 emails to contacts for which I know I have working email addresses!! (I know they are working, as I am able to send personal emails to these addresses from my gmail account)

Please advise?

Thanks,
David