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When using OpenSSL on Ubuntu 20.04 I'm not able to connect to any ports other than 80 and 443. When I try to connect to any other port, for example 587, the script hangs and I get no output at all and I have to CONTROL-C to kill the script:

// this works
$ openssl s_client -connect postmarkapp.com:80
$ openssl s_client -connect postmarkapp.com:443

// this does not work
$ openssl s_client -starttls smtp -connect smtp.postmarkapp.com:587

I thought it might be a certificates issue but I've updated those and the issue hasn't improved:

$ sudo apt-get install ca-certificates -y
$ sudo update-ca-certificates

Everything on this machine is updated to the latest packages, of course.

I checked my firewall, even turned it off entirely, and I still can't make any outbound connections to any site on any port other than 80 or 443. I tested other versions of Ubuntu and this same issue is on 18 but not on 16.

Any help appreciated.

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  • Check your firewall and any external firewalls. Mar 9, 2021 at 22:04
  • Are you able to connect with telnet smtp.postmarkapp.com 587? Mar 11, 2021 at 13:50

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