Massive eMail Spamming with Default event invite template "You have been invited to $fp_events_name"

We have a Ubuntu VM (Hyper-V) running the latest Suite Stable build. Note this is a relatively new installation (3 months) and still in the implementation stages.
We have both Inbound/Outbound/Bounce settings enables with an Office365 email.
It seems that any time we start the server vast amounts of emails are sent through the SuiteCRM server. It seems that the email addresses are random and not necessarily within the CRM DB.

Could someone here give me some pointers as to where to start looking to resolve this issue? We believe this is the solution we need but obviously cannot send spam through our server.

Thank You.