Email bombing

We’ve seen this type of DoS attack (denial of service) as a cover for compromising related financial accounts like Paypal.  Typically they are verification or confirmation messages from various sites.  They aren’t actually spam since they are valid messages, they’re just triggered by someone else using your e-mail address.  They count on the flood of spam hiding any warning or alert messages from the other sites.  I would strongly suggest you check all such sites now (if not sooner) to make sure they are safe and secure.    https://support.google.com/mail/answer/1366858#mailbomb 

 

As to the attack itself, the flood of messages should slow and eventually stop after some days.