Gmail couldn't verify that domain.com actually sent this message (and not a spammer)

Gmail couldn't verify that domain.com actually sent this message (and not a spammer)

Hi, I have multiple client domains hosted in Zoho. When I send emails from zoho to gmail accounts, I am getting a question mark place holder over the user image and when I mouse over it reads "Gmail couldn't verify that domain.com actually sent this message (and not a spammer)". One thing to keep in mind which i am not sure if it is related is all of my client domains  are being used along side with Mandrill for sending html emails. I am not sure if they are related. Only DKIM and SPF records are defined in DNS for those domains for mandrill. Any ideas?