Cannot deliver email campaigns to emails hosted on Microsoft Exchange

I've created a few test email campaigns and tried sending them to my co-workers. They were marked as delivered in Zoho Campaigns; however, no one received the campaign (not even in junk email folder). We use Microsoft Outlook for email. After another test, one person out of 4 got the campaign email in Exchange... in junk mail.

Emails to other hosts were received (yahoo mail and gmail). However, the message sent to gmail was automatically put into the spam folder. How do we avoid this in the future?

Not sure what to do. I followed the tips described in the help section and this was the result.

Sandy