Error sending email to external address

[Simius]

Hello,

sending e-mail via pop3 or php to some external email addresses result in the following error in the qmail log:
Oct 5 09:12:25 server qmail: 1191568345.113758 delivery 4954: failure: This_address_no_longer_accepts_mail./

The emails address are working for sure...
Any clue?

In the log i can also see this:
Oct 5 09:12:25 server qmail-local-handlers[32707]: [email protected]

I don't know were it takes the anonymous name for the pop3 (i can fix this in php)

Thanks you