sendmail : mail not delivered

[Felipe Nunez]

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 at hotmail.com  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 at bizet.sys.linux>, relay=felipe at localhost
Mar 21 20:03:38 gatopardo sendmail[6929]: l2M03bga006929: 
from=<felipe at bizet.sys.linux>, size=907, class=0, nrcpts=1, 
msgid=<200703220003.l2M03ati006928 at bizet.sys.linux>, proto=ESMTP, daemon=MTA, 
relay=localhost.localdomain [127.0.0.1]
Mar 21 20:03:38 gatopardo sendmail[6928]: l2M03ati006928: 
to=rfnunez at hotmail.com, 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 at hotmail.com>, ctladdr=<felipe at bizet.sys.linux> (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 at bizet.sys.linux>, 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