I have a client that uses SharePoint Online but insists on using Gmail. Each user has a O365 account with an Exchange Online mailbox and mail flow/delivery options are set to forward all incoming mail to the corresponding user's Gmail address.
From Monday (08/10/2018), all forwarded mail from firstname.lastname@example.org (the default from-address of SharePoint Online used for alerts and workflow email) has ended up in the Spam folder of each user's Gmail account. The same happens when forwarding to a @outlook.com account.
It appears that the forwarded mails are failing DMARC so are being quarantined by the recipient mailbox.
Authentication-Results: spf=pass (sender IP is 126.96.36.199) smtp.mailfrom=mytenant.onmicrosoft.com; outlook.com; dkim=pass (signature was verified) header.d=mytenant.onmicrosoft.com;outlook.com; dmarc=fail action=oreject header.from=sharepointonline.com; Received-SPF: Pass (protection.outlook.com: domain of mytenant.onmicrosoft.com designates 188.8.131.52 as permitted sender) receiver=protection.outlook.com; client-ip=184.108.40.206; helo=EUR01-DB5-obe.outbound.protection.outlook.com;
The way I understand it, DKIM and SPF are passing but DMARC is failing because the header.d address does not match the header.from address.
Is that about right? Is there any way around this? Is there some way I can "whitelist" the sharepointonline.com domain so that these forwarded mails are no longer quarantined?
I don't fully understand how all this works but shouldn't this not be a problem as mytenant.microsoft.com and sharepointonline.com are both MS-owned domains?