Sendmail relay problems

[trialex]

Hello everybody.
I came across this problem many times while installing slackware and trying to set sendmail as my mailserver.
I know for sure that there is a solution to it even though I cannot remember it each time I try a fresh install.
I also know that it is very simple.
Here comes the problem.
Sendmail cannot send emails to hotmail,yahoo etc.
My isp is comcast and I use it's smtp as my smarthost. I know all the theory about blacklists and authentication, everyone admits that it is impossible to workaround this issue but I know for a fact that I was able to send/receive to those accounts at the past.
I remember that I had to disable "named" from running on my box to have sendmail receive but that was one part of the solution. Another part was that I had to cut off the hostname from my FQDN host file for sendmail to receive emails, but still something is missing to send .
Anyone has a clue?
I will appreciate any help.
Thank you.

[kern]

have you checked the logs? or used sendmails test function?

[trialex]

Thats what I get in maillog:

Oct 16 13:38:58 robotblues sm-mta[3325]: k9G3YAEC005277: k9GKcvgM003325: sender notify: Warning: could not send message for past 4 hours
Oct 16 13:38:58 robotblues sm-mta[3325]: k9GKcvgM003325: to=<root@robotblues.net>, delay=00:00:00, xdelay=00:00:00, mailer=esmtp, pri=31618, relay=robotblues.net., dsn=4.0.0, stat=Deferred: Name server: robotblues.net.: host name lookup failure
Oct 16 13:38:58 robotblues sm-mta[3325]: k9G3BCgC004198: k9GKcvgN003325: sender notify: Warning: could not send message for past 4 hours
Oct 16 13:38:58 robotblues sm-mta[3325]: k9GKcvgN003325: to=<root@robotblues.net>, delay=00:00:00, xdelay=00:00:00, mailer=esmtp, pri=31627, relay=robotblues.net., dsn=4.0.0, stat=Deferred: Name server: robotblues.net.: host name lookup failure
Oct 16 13:38:58 robotblues sm-mta[3325]: k9G32bou004069: k9GKcvgO003325: sender notify: Warning: could not send message for past 4 hours
Oct 16 13:38:58 robotblues sm-mta[3325]: k9GKcvgO003325: to=<root@robotblues.net>, delay=00:00:00, xdelay=00:00:00, mailer=esmtp, pri=31629, relay=robotblues.net., dsn=4.0.0, stat=Deferred: Name server: robotblues.net.: host name lookup failure


I try to test sendmail by telnet and I get no errors.But my email don't reach hotmail accounts.
Thank you

[idle]

you say you can't send to certain mail servers such as yahoo and hotmail, but you don't mention if there is anywhere you *can* send mail to.

looks like you have a DNS problem, so need to look at your /etc/resolv.conf to see if it is pointing to legitimate DNS servers.

if you can send internally, but not externally, it probably means that you are able to send to hosts listed in your /etc/hosts, but anything external will fail.

I don't know why disabling named would stop sendmail receiving mail, unless it's misconfigured. Or perhaps you have a firewall that is not allowing you to make DNS queries outside your network...

[trialex]

I can send email to gmail accounts and internal accounts as well.
My resolv.cf points to comcast servers.
My "hosts" file has the loopback and my domain name from which I cutoff the hostname that precedes it.
ie: from "hostname.domain.net" then "hostname" to just "domain.net" "hostname".

Finally I have to say that all my internal accounts can send/receive to each other, can send/receive to gmail, but cannot send but can receive from "hotmail,yahoo etc."

Does this description help?
Thank you.

[trialex]

Plus I don't use firewall at this point.

[idle]

you should leave the FQDN in /etc/hosts as that file links IP addresses and hostnames. But it's also a way of configuring aliases, so if your domain name also points to your IP address, then it's safe to leave that in there as a third entry.

however, the logs you posted showed that you can't connect to robotblues.net because you can't resolve the DNS name.

Are you hosting your own domain? If so, how is your DNS configured?