" This message is not RFC 5322 compliant " error notification

Products

• Email Security.cloud

Issue/Introduction

Antivirus notification to Google fails with error "This message is not RFC 5322 compliant , There are multiple To headers".

The following message: "550-5.7.1 This message is not RFC 5322 compliant. There are multiple To headers. 550-5.7.1 To reduce the amount of spam sent to Gmail, this message has been 550-5.7.1 blocked."  Messages (like the Anti-Virus notification) with multiple recipients were being interpreted by Gmail as having multiple "To:" fields rather than multiple recipients within a single "To:" field.

Environment

Email Security.cloud

Cause

This is caused by Google policy

Resolution

It is recommended to refer to article of Google Knowledge Base

https://support.google.com/a/answer/13567860?hl=en