We have an error with a various domains with sending e-mails. Our server returns with the message :

Jan 22 10:15:00 correu postfix/smtp[5100]: 5F17239EC02C: to=<comunicacion@tenisgimeno.com>, relay=mail.tenisgimeno.com[]:25, delay=0.18, delays=0/0/0.1/0.07, dsn=5.0.0, status=bounced (host mail.tenisgimeno.com[] said: 501 Domain must resolve (in reply to MAIL FROM command))

I don't know what is the problem. Any idea?