If you received tens of hundreds of mail bounce messages from emails you didn't originally send, then you may be a victim of email spoofing. Similar to the way postal mail works, when you write your return address on an envelope, the postal system knows to return mail to you if the recipient is not valid. This method works the same in email servers. A spammer will use your email address as the return to email, and when a spam message bounces, it goes to you instead of the original spammer.
Because these messages originate outside of OnePointSync, we aren't able to stop spammers from spoofing your address. However, we help protect your email address's reputation by designing our systems to authenticate all the mail that really comes from you. When another domain receives an unauthenticated message from OnePointSync, it can tell that you didn't really send the mail, and it is unlikely that your email address will be blocked.
If you feel that you may be a victim of identity theft, we suggest contacting your local authorities.