I currently have exchange 216 with DAG, last week I installed an exchange 2019 servers. I heard it can co-exist, so I set both exchange 2016 and 2019 server's VS to https://webmail.domain.com/ for all external and internal urls. Also put all exchange 2016 and 2019 in to F5, using F5's exchange iAPP. All exchange 2016 and 2019 are on the same iAPP VS. After that, I was getting a cert error autodiscover was randomly giving out exhange19.domain.com for internal VS name, I recycled auto discover app pool on all servers and the cert error went away. About 10 to 15 minutes later outlook could not connect, it was in disconnected status , connection status showed exchange directory was connected but having trouble connecting exchange mailbox. it kept on trying and after about 5 minutes later it got connected. Problem was it happening randomly. I rebooted all exchange 2016 and 2019 servers one at a time, still the same. I disabled exchange 2019 from F5 still the same problem. I setup a lab with almost same configuration using virtual servers, and lab outlook connects without problem. I looked at all evet logs and exchange logs but could not find any thing stood up, I ended up uninstalled exchange 2019, and everything came back normal. Questions: 1. Can exchange 2016 and 2019 server have same exchange VSes? eg: https://webmail.domain.com/owa, https://webmail.domain.com/ews etc? 2. Can exchange 2016 and 2019 servers be on the same F5 and same VS? 3. If 1 and 2 are not supported, why my lab exchange servers work? 4. If 1 and 2 are supported, what am I doing wrong? 5. Does any exchange 2016 or 2019 use IPv6? I disabled them. Thank you in advance.