Unknown Office 365 Mailbox Shows High Send Usage

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?
GISCOOBYDirector of Information TechnologyAsked:
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Vasil Michev (MVP)Commented:
That's a system address, used to generate NDRs and some other messages. You can get the info via

Get-OrganizationConfig | fl MicrosoftExchangeRecipient*

MicrosoftExchangeRecipientEmailAddresses            : {SMTP:MicrosoftExchange329e71ec88ae4615bbc36ab6ce41109e@michev.onmicrosoft.com}
MicrosoftExchangeRecipientEmailAddressPolicyEnabled : True
MicrosoftExchangeRecipientPrimarySmtpAddress        : MicrosoftExchange329e71ec88ae4615bbc36ab6ce41109e@michev.onmicrosoft.com
MicrosoftExchangeRecipientReplyRecipient            :

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More info here: https://technet.microsoft.com/en-us/library/bb430759(v=exchg.141).aspx
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