A few days before there was an interruption of my forum operation. After restoration started another problem concerning the e-mailing operation. Now the forum email seems not to work and every notice returns as a failure message. In one day i have more than 800+ undeliverable e-mails ... f.e. "This message was created automatically by mail delivery software. A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed: firstname.lastname@example.org retry time not reached for any host after a long failure period" And follows the content of the notice. Host informed me three days ago to change the current nameservers with some new ones. I haven't change them yet, is this possible to cause this problem? There is a big problem because many members get informed by email notices for replies, watching threads, etc and when they see that they have posts without noticing they are complaining.