So, I've done a fair amount of digging and I can't find a real resolution for this. One of my users asked me to look into why she was getting an error message when she sent an SfB message to a client that uses the same service. I figured it was on the client's side since we (the organization) and she are both setup to communicate with all external domains that aren't blocked. This morning I found out the client can't even see that we're online, so there's 0 communication there. I ran some tests with a few different Skype & SfB accounts and wasn't able to get them to talk. So now it's our problem.

Nov 14, 2018  If the Skype for Business on Mac user also cannot send or receive from others, let him/her to contact their Office 365 admin to check if the user has valid Skype for Business Online License or if they can receive messages from users outside their domain. Users of the Windows client see 'This message wasn't sent to.' When messaging with users of the SfB Mac client. We do not have the issue when the Mac end is running the previous 'Lync' client. I have been playing around with Skype for Business Hybrid and getting Office 365 Cloud PBX calling happening. Anyway, during the setup of the environment I hit a snag and couldn't get users in on-prem seeing users in the cloud. It was an interesting one as cloud people could see presence for On-Prem. Skype for Business on Mac users can't search the Skype directory, although you've enabled this functionality for your organization. However, Skype for Business on Mac users can communicate with Skype users if they know the Skype user's Microsoft account.

THEN.the service tech comes in and tells me another user is able to communicate with the outside world. This prompted another test. I added him as a contact from SfB and I'm now able to communicate with his Skype account. He added me as a contact from SfB and there's radio silence. No communication.

We are both have current updates for MS Office 2016, Skype & WindowsX. Adobe flash player for mac. We are both on the same LAN & both have the exact same firewall restrictions/provisions. Yeah.I'm at a loss for what to do next. All configurations seem to be in order, MS O365 connectivity & DNS tests were fine. There has to be a valid reason (and therefore a fix) for this, right?

I'm interested and confused about the user that can communicate with the outside world. Is he in another Office 365 tenant or the same tenant with you?

You mentioned you can communicate with his Skype account. So, you added his Skype account, not the Skype for Business account? He added your SfB account via SfB or Skype? Generally, for SfB external communication: 1. For communication between 2 different Office 365 tenants, you need to make sure both tenants enabled external communication. You can turn off external communication of your tenant temporarily. After waiting about 1 hour, turn on again to see if it works.

Apple remote deployment tool for mac os. Red.foxx15 - thanks for the heads up. Unfortunately this is the only information I've been able to find concerning external communication errors with SfB. It's like MS thinks every administrator is too dumb to mean it when they say something to the effect of, '.we (the organization) and she are both setup to communicate with all external domains that aren't blocked.' This was the first thing I checked and it was set correctly. We are both on the same tenant. Yes, that's correct.

I added his Skype account to my SfB account. It was a test. He added my Skype account via SfB. This was also a test. Yes, I'm aware. I read somewhere (MS rep on technet) that it could take a few days for changes to this setting to take effect. Why do you suggest I wait an hour and turn it back on?

Why (stupid question incoming) is this part of the troubleshooting process? If this were the fix, do you have some powershell scripts available that would accomplish the same goal without having to rely on the GUI or the potential of cutting the few that can communicate with the outside world off from speaking with their customers?  *Edit: grammar. Claud (Microsoft) wrote: Given this situation, I suggest turn off external communication of your tenant in a non-peak time period. As for one hour, it is based on my working experience.