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I have a SMTP server on a Windows server 2008 R2. It can send messages to all other domains except the ones hosted at Microsoft (hotmail.com,outlook.com, etc). The email messages it cannot send remain in: \mailroot\Queue. Also the logs only show the following:

127.0.0.1, SERVERNAME, 4/25/2016, 15:13:13, SMTPSVC1, SERVERNAME, 127.0.0.1, 0, 9, 226, 250, 0, EHLO, -,  SERVERNAME,
127.0.0.1, SERVERNAME, 4/25/2016, 15:13:13, SMTPSVC1, SERVERNAME, 127.0.0.1, 0, 27, 40, 250, 0, MAIL, -,  FROM:<[email protected]>,
127.0.0.1, SERVERNAME, 4/25/2016, 15:13:13, SMTPSVC1, SERVERNAME, 127.0.0.1, 0, 33, 36, 250, 0, RCPT, -,  TO:<[email protected]>,
127.0.0.1, SERVERNAME, 4/25/2016, 15:13:13, SMTPSVC1, SERVERNAME, 127.0.0.1, 0, 50358, 141, 250, 0, DATA, -, <[email protected]>

Messages to gmail look exactly the same, except the destination is some hotmail/live/outlook address.

Ive also check my SPF records and they check out, else gmail wouldve already blocked the messages.

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    What happens if you try sending a test mail from the server using Telnet? It might show that the remote server rejected it.
    – smwk
    Apr 25, 2016 at 15:27
  • It looks like we are blacklisted at Microsoft (not sure but most likely). random telnet to a gmail account worked, but the exact message to hotmail.com failed without telling us why. Ive submitted a delist using: link
    – TheGreenOrange
    Apr 26, 2016 at 9:43
  • Seems the most likely cause, let us know how you get on.
    – smwk
    Apr 26, 2016 at 10:34
  • Some good info here - serverfault.com/questions/772045/…
    – smwk
    Apr 26, 2016 at 14:16

2 Answers 2

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Found out it(after I checked two other SMTP servers sending an email to hotmail.com worked) had something todo with the second NIC not being configured (DHCP on) and the SMTP server used it for its outgoing traffic (firewall didnt liked that). After disabling it, clearing the DNS and checking nslookup again it got the right address and started processing the MS related emails. It still doesnt explain why everything else worked... but at least got it working again.

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@TheGreenOrange

When you telnet to hotmail, you can't simply do 

 telnet hotmail.com 25

You have to telnet to their MX Records (Which is their Mail Servers) and they have a lot as you can see: Hotmail MX Records

Take the one with the lowest preference

telnet mx1.hotmail.com 25

Wait like 20 seconds for a reply. If it doesn't time out then you know your not being rejected/greylisted at that level. If you do connect you can send an email though command-line and see what happens.

Another good test will be to send a test email to [email protected] - to see what criticals shows up on their report.

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