Unable to communicate through Skype for Business with other Skype users


We have Skype for business on-premises setup and use office 365 for emails.

However, we are having problems with contacting Skype  users from our Skype for business app. I have tested sending invites but they are not getting to the users both ways. I can search Skype users which appears but when send and invite nothing gets sent.

Have made sure that Skype admin is setup so that  external communication is set to "On except for blocked domains" is there something that I have missed?

I have tested connection with other organisations also using Skype for business, that seems to be working for some organisations but not all, but I think that they need to add us into there allowed domain list. Any help would be much appreciated.

Keith BuiAsked:
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Did you check the event logs on the server ? are you getting any kind of error while sending messages ?
Keith BuiAuthor Commented:
Nothing at all
I'm having a similar issue. We can seem to call anyone outside our organization even though in O365 global admin settings we have it set to allow everyone. I called MS support and i was able to Skype them so they claim its working but but nothing i've done has helped.

do you know what your settings for Skype say in the global admin settings?
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Keith BuiAuthor Commented:
We currently have "On except for blocked domains"  on the Office 365 admin and ticked " "Let people use Skype for business to communicate with Skype users outside your organisation."

Do you think we need to add the following to the firewall:
.api.skype.com, *.users.storage.live.com, and graph.skype.com
Keith BuiAuthor Commented:
Got it working by registering our domains with https://pic.lync.com,

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Keith BuiAuthor Commented:
All good now
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