I didn’t send mail to those recipients. Why I get so many return message suddenly?
Spammer also usually use a fake "To" and "From" address, a practice called "spoofing." If the fake address they use for that purpose happens to belong to someone, it usually results in a denial of service attack against the innocent person, as tons of complaints and bounced mails begin flood that person’s inbox.
We are sorry that Communilink could not stop this kind of spam activity as the spammer would not use our SMTP to send out mail. Please still call us if you encounter this problem and see if we can help to stop the return failure notice for you.
Also, you can find below attached PDF’s News about spoofing.