Hi: I have being using sendmail as long as I have being using Linux, that is, some years now. But in the past months I've got some problem when sending mail to some particular email-adresses. Mail just get returned, just from those particular mail servers/ If , for example, I send a mail to rfnunez@xxxxxxxxxxx it can read from /var/log/maillog, something like: Mar 21 20:03:37 gatopardo sendmail[6928]: l2M03ati006928: from=felipe, size=613, class=0, nrcpts=1, msgid=<200703220003.l2M03ati006928@xxxxxxxxxxxxxxx>, relay=felipe@localhost Mar 21 20:03:38 gatopardo sendmail[6929]: l2M03bga006929: from=<felipe@xxxxxxxxxxxxxxx>, size=907, class=0, nrcpts=1, msgid=<200703220003.l2M03ati006928@xxxxxxxxxxxxxxx>, proto=ESMTP, daemon=MTA, relay=localhost.localdomain [127.0.0.1] Mar 21 20:03:38 gatopardo sendmail[6928]: l2M03ati006928: to=rfnunez@xxxxxxxxxxx, ctladdr=felipe (601/600), delay=00:00:02, xdelay=00:00:01, mailer=relay, pri=30613, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (l2M03bga006929 Message accepted for delivery) Mar 21 20:03:52 gatopardo sendmail[6931]: l2M03bga006929: to=<rfnunez@xxxxxxxxxxx>, ctladdr=<felipe@xxxxxxxxxxxxxxx> (601/600), delay=00:00:14, xdelay=00:00:14, mailer=esmtp, pri=120907, relay=mx2.hotmail.com. [65.54.244.168], dsn=5.0.0, stat=Service unavailable Mar 21 20:03:52 gatopardo sendmail[6931]: l2M03bga006929: l2M03qga006931: DSN: Service unavailable Mar 21 20:03:52 gatopardo sendmail[6931]: l2M03qga006931: to=<felipe@xxxxxxxxxxxxxxx>, delay=00:00:00, xdelay=00:00:00, mailer=local, pri=32158, dsn=2.0.0, stat=Sent So, I wonder what does DSN (Delivery Status Notification) is all about.And what can I do to continue sending mail to all addresses as before ? F N