Using Office 365 for Exchange. As I looking through my Security & Compliance reports I see a mailbox with the second highest send count as an unrecognized mail sender. The address is formatted as MicrosoftExchange329e71ec88ae4615bbc36ab6ce41109e@DOMAIN.onmicrosoft.com. I tried looking through the Audit Logs and searching for this account using PowerShell for the email address as listed and only the GUID, but I have found nothing. I do have a shared mailbox that is used for Constant Contact distribution but the GUID does not match. Strangely enough, I don't see this shared mailbox listed in the Top Mail Senders list at all. Can someone please help direct how I can find out what this account represents?