Emails classified as Spam Office 365 - Reasons and recommendations

Emails classified as Spam Office 365 - Reasons and recommendations

We noticed that the emails from some of the accounts in Zoho Mail end up in Spam folder for recipients using Office 365 email. The issue is caused due to Exchange Online Protection server in Office 365, wrongly identifying a genuine email from Zoho Mail as Spam, i.e, due to a case of 'false positive' in EOP. This issue caused our IP range to be classified as Spam, and hence all the emails from those IP addresses were classified as Spam by Outlook (Office 365) servers. 

Our engineering and abuse monitoring team identified the root cause quickly and our team escalated this with the Outlook service team raised as Severity Level 1 issue. We did not receive any significant complaint via the FBL (Feedback Loop), which is generally used by Email service providers (ESPs) like us to address the abuse complaints/ issues before blacklisting the domain or IP address. 

Outlook team have also acknowledged that the emails were wrongly classified as Spam and they were false positives. They have promised a resolution within the next 48 hours.  You can further request the admins to add Zoho's IP range 135.84.80.192/26 and 136.143.188.0/23 to their connection policy in Office 365, using the instructions available here. After the admin completes this step, the emails will get delivered. 

The above workaround is temporary and is to address the users who frequently email to a particular domain or email account in Office 365. We are in touch with the Office 365 team to resolve the issue permanently. The issue can now be resolved only by the Outlook team, by removing our IP address range from their black lists. 

We appreciate your patience and cooperation.  

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