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/SMTP connection failure/

SMTP connection failure

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I have been working with a windows 2012 virtual desktop and the SMPT server does not connect to port 465 from the Telnet session.

2 Answers
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Port 465 is by default SMTPS (SMTP over SSL), which is encrypted. So You cannot communicate with it via Telnet.

Can you provide more information on the issue? E.g. is It a connection timeout issue? or is there any error message you received?

answered 21 days ago
  • Hi Richard, Thanks for your feedback. The error message when connecting to the 465 port using the smtp.office365.com server is Could not open connection to the host, on port 465: Connect failed.

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Hi Zac,

It would have helped if you specified the exact error you got.

SMTP traffic is ussually blocked by your security groups or NACLs settings. To allow traffic over this port, please review the following:

  • The security group outbound (egress) rules must allow traffic to the SMTP server on TCP port 465.
  • The network ACL outbound (egress) rules must allow traffic to the SMTP server on TCP port 465.
  • The network ACL inbound (ingress) rules must allow traffic from the SMTP server on TCP ports 1024-65535.

Also make sure that your Windows virtual desktop firewall and antivirus application allows traffic to SMTP server on port 465. Additionally, please make sure you verify the following:

  • Kindly check application side configurations as well that it was properly configured or not.
  • Next try to telnet to port 465, if it still fails please run the below command to check if any other service is using port 465:
netstat -ano | find "465"

For assistance with analyzing the output of the above command you can reach out to me, I will be willing to assist. I hope this helps

answered 21 days ago
  • Hi Cebi, Thanks for your feedback. The netstat command does not give any output.

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