Hotmail problem

Really need some ideas and help!
We are not able to send email to any Hotmail account anymore.
Anyone who knows what all Hotmail are filtering?
I set up my own test account with Hotmail, tried a regular telnet session from one of our servers.

Mail From - OK
Rcpt To - OK
Data - Mail has been queued for delivery...

And still I don't get anything to my hotmail account, not even to my junk folder. Also added our domain to the "Trusted" list on my Hotmail account.

Tried to do the same telnet session from home, and it all works fine.. !

Wonder if our College has ended up on a blacklist or something? Anyone knows where to check, if Hotmail is checking against blacklists?

Or could something completely different be going on??

Thanks in advance!!

Did you check your inbox from another PC or internet connection?
I wonder why do you still stuck to hotmail????
Many friends of mine complained about the same problems.... sounds they are encountering a problme or something...
Everyone usues Gmail!!
I have forsaken hotmail forever....
Gmail is the best.. if you want an invite do ask...
Cheers

well to make a long story short , ihave been a hotmail client for 2years now and i use it every now and then just because of the fact that you are only allowed 2 mb as a normal user.I went over to webmail in south africa and got a 10mb account without having to upgrade to a permanent account.I am South African of course so..ya I think for all the temporary clients they have got the could certainly make an attempt to increase their account limit.In your case i think it is worth trying a different service.

cheers
vanman

Sorry, I guess I didn't give enough background.

I'm not the Hotmail client, our users are.
We are a College, with several hundreds students using Hotmail, and we have services and applications sending email notifications to the students.

So I need to actually figure out what the problem is, sending email to Hotmail accounts.

Thanks for your comments though!

Oh and Yes, I did check the inbox from another location, still no good.
I'm also getting postmaster notifications back saying:

Delivery Status Notification (Failure)
Action: failed
Status: 4.4.7

Any other ideas!?

Do you use a free email accounts to send email to your students??
If not, what email client reader to you use??
Is this case generic, happens when sending to email other than Hotmail??

Thanks for your quick replies! :)

No, not sending from any free email. We have our own GroupWise mail server.
But it has nothing to do with that either, since I'm able to replicate the problem making a direct connection to the Hotmail server with a Telnet session, like I described in my first message.

As far as I can tell, Hotmail are the only ones we get undeliverable email notifictaions...

Really appreciate your help!
Any other ideas?

sounds like your mail server's been put on a black-hole list.

Yes, I'm afraid we have ended up on a Black-hole list somehow...
Anyone knows if Hotmail is checking any specifc Black-hole lists?
Or what are some common/good Black-hole list sites to check if we are added?

Thanks!

http://www.spam-blockers.com/SPAM-blacklists.htm

I'm confused about the telnet part. Did you telnet to hotmails mail server and try to send a message? I surely hope this isn't possible, as that would constitute them having an open relay themselves. If you do that you mail should be lost. If you telnet to your own server on 25 and send a message what happens?