When Gmail views some practices of your sender domain as suspicious or when the reputation of your sender domain decreases beyond a particular threshold, all emails from your sender domain will be moved to spam and users will receive the following message:

" Why is this message in spam? Lots of messages from yourdomain.com were identified as spam in the past"

The following are a set of possible scenarios which may have lead to the above notification. Make sure to avoid these practices in the future:

• Usage of sender address from a secondary domain (other than the domain of your official website) can be reduced, as your email recipients may not recognize the relationship between the two different domains. If you still want to use a secondary domain, make sure to include the signup URL in the footer of the email for your recipient to verify the connection between the domains.
  

• The subject may not convey the message you actually intended to deliver to your email recipients. Due to this, they may feel mislead and mark you as spam. Ensure that your subject and content are relevant to each other.
  

• Zoho MarketingHub strongly recommends that you follow permission-based email marketing. Ensure that all of your leads have opted in to receive your newsletters.
  

• The mailing list may contain old contacts with which there has been no communication for a significant duration (at least three months). When you send an email after a long time, they might not recognize you and hence may mark you as spam. Convert inactive into opt-in contacts by sending re-engagement emails. Further emails must be sent only upon receiving their consent, as mentioned in the previous point.
  

• If you have sent various campaigns in a short amount of time, then the inbox of your recipients may have been flooded, thereby creating more chances of marking your emails as spam. Always give regular intervals between your consecutive campaigns.
  

• Seeking sensitive information in the content of the email itself or in an immediate landing page from a URL is considered spam triggering. So, your email recipients may have felt it suspicious. If it is necessary to collect sensitive information, then you can add an optional step to ask such details while your they sign up.
  

• Usage of certain words in content/subject such as buy, order, discount, clearance, dear friend, as seen on, please help, free, offer, desperate, additional income, etc may result in marking of spam. These words may raise the suspicion of either your email recipients or Gmail. It's strongly recommended to avoid usage of spam-triggering words in both subject and email content.  
  

The reputation of your domain might have been reduced due to any of the above scenarios. There are some suggestions from our deliverability team. Senders can make use of the given suggestions to avoid further decline in their domain reputation.

• Gently remind your subscribers to add you to their contacts, so that you can be one-hundred-percent sure that your emails land in their inbox.
  
Ensure that your domain has a good reputation in Gmail by using  Postmaster Tool   to analyze your email performance, its reputation, and other vital factors. Using this data, you can realize the current status of your domain reputation and act accordingly.

• Incorporate the following lines as footer data while sending out email campaigns, especially while sending to Gmail users: 
  

1. If you see this email in your spam folder, kindly add us to your contacts for our regular communication.
   
2. If you are not interested in receiving our emails, you can unsubscribe.
   
3. If you see this email in the Promotions tab, kindly drag and drop it into your Primary tab so that our future emails will arrive in your inbox.
   
4. You're receiving this email as you have signed up with us at "sign up URL".