If all of the following conditions exist in your company, e-mail sent from Microsoft Exchange Online to your company’s distribution groups may be filtered as spam and not delivered. Why does this happen? Distribution groups have an Active Directory property called ReportToOriginatorEnabled. This property can have a value of True or False. If set to True, the e-mail system receiving the mail will be able to read where the mail is coming from; if False, the receiving e-mail system will not be able to tell where the mail is coming from. Workaround: To ensure delivery of e-mail, set the value of the ReportToOriginatorEnabled property to True for all distribution groups in your on-premises e-mail system. You can do this with LDP.EXE, ADSI Edit, or a script that can modify the ReportToOriginatorEnabled property. After you make this change, this property will be updated in Exchange Online at the next synchronization.
Source:→ MOS Blog