External users cannot connect to our Skype for Business 2015, Internal users are fine

When I use The Microsoft Connectivity Analyzer for Skype for business connectivity I get an error when it is attempting to obtain the SSL certificate from remote server. please see attached.
Montana ManIT SupportAsked:
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Andrew LeniartFreelance JournalistCommented:
The SSL certificate wasn't purchased from Godaddy by any chance, was it? I've seen lots of this type of error being reported when using a GoDaddy supplied certificate.

Also, try enabling TLS 1.0 and disabling firewall temporarily, then see if the certificate will download. Both of those have solved similar problems for others, albeit not for Skype, but identical errors reported. A firewall rule exception has needed to be added.

Kemp Support Centre (See last post by "steven")
Spiceworks Thread (See post by Bryce Katz)

Hope that's helpful.

Regards, Andrew

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Craig BeckCommented:
Might sound like a daft question but is external access configured?
Blue Street TechLast KnightCommented:
Hi mogurek,

Can you expand all the arrows under the Additional Details for both errors from your attachment and re-post them. That's where goodies lie.
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