Hi Zoom Support, 

I had sent the invitation to the users below, but they have not received the invitation email for the zoom. Would you please check if those emails were on the bounce back rule or black listed?
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Hi,
Failed to add two specific email addresses. An activation email was just not sent to them.
According to a check in the firewall, the email is not blocked and does not enter spam. IPs 198.2.179.123, 198.2.179.168 and 198.2.179.86 already in whitelist in FW. I also do not see any attempt in logs to open incoming session from these addresses. 
All other users in the same domain have successfully activated their accounts.
I also have two extra licenses so it is not a problem of licenses.

I have been teaching piano/keyboard lesson using Zoom, as well as given many lectures for Yamaha using my digital piano. Last Wednesday and Thursday I was unable to hear my students instruments, and they were unable to hear mine. I would hear about 4 notes, then everything was gone. I could hear them speaking perfectly, but no instruments. I use a Windows 10 computer, and all students were on iOS devices. I pay extra for this service, and don't use the free service. What has changed, and what do I need to do to be able to teach successfully again? This is a real problem. Thank you! Lori

Even starting this topic is frustrating! I was trying to do a webinar today but because of the echo and reverberation, had to cancel a presentation minutes in. I have a MacBook and in order to play audio not only from myself but from the Keynote presentation I have used Loopback flawlessly until recently.

Got error code 10004 so I uninstalled and reinstalled Zoom. Still SIGNIFICANT echo and reverberation. I need to be able to use audio from my mic, Keynote and Quicktime player for audio and video - WITHOUT echo and reverberation. 

Can anyone help solve the problem, or does anyone know of a company/person that could troubleshoot these issues for me?

Thanks,