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Export StartTLS certificate from SMTP server

While configuring Office365 as the messaging (SMTP) server within Aruba ClearPass, I needed to upload the certificate from the StartTLS session to the certificate trust list from ClearPass. I had to export the certificate for smtp.office365.com via the following OpenSSL command:

openssl s_client -showcerts -starttls smtp -crlf -connect smtp.office365.com:587

After running the command, you will see some output like shown in the image.

openssl starttls

I copied the both parts between BEGIN CERTIFICATE and END CERTIFICATE to two different text editore files and saved them with the extension .cer. Next I was able to upload both certificates to the certificate trust list in ClearPass and configure the message server with StartTLS Connection Security

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René Jorissen

Co-owner and Solution Specialist at 4IP Solutions
René Jorissen works as Solution Specialist for 4IP in the Netherlands. Network Infrastructures are the primary focus. René works with equipment of multiple vendors, like Cisco, Aruba Networks, FortiNet, HP Networking, Juniper Networks, RSA SecurID, AeroHive, Microsoft and many more. René is Aruba Mobility First Expert (AMFX #26), Aruba Certified Mobility Expert (ACMX #438), Aruba Certified ClearPass Expert (ACCX #725), Aruba Certified Design Expert (ACDX #760), CCNP R&S, FCNSP and Certified Ethical Hacker (CEF) certified. You can follow René on Twitter and LinkedIn.

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