We have few sites where all sites are working fine and no issue but only one site has problem and problem is that users are good and using outlook and exchange services but suddenly they get disconnected and outlook trying to connect where all sending email is are pending in outbox(this site is connected with VPN to primary(Exchange server), let me explain what i did so far,
1. Checked VPN route (working fine all traffic, pend, tracert and nslookup all works fine)
2. host file was edited where the traffic was forwarded to external DMZ i edit and everything became normal and i thought the problem is solved but after three days this issue is back.
3. i was working to troubleshoot and couldn’t find anything wrong (when i am tracert my email server from client machine it reaching the server no packet drops, when i am access webmail its working everything is ok but still all users outlook trying to connect and users are not able to send or receive email.
4. troubleshoot DNS on client's machine all works fine but not outlook.
5. All sites are connected to same server and everting one is able to use the services expect this one site.
6. today when i troubleshoot almost 80% of users were able to access the services but 20% of them not.
7. All these users are able to send and receive email with their mobile or web-mail resources.
8. few days ago I change or renew SSL certificate I am sure this won’t make any issue because it’s with same information…..
Also, make sure the updated certificates are properly reflected on any other Exchange servers that are also communicating with the original Exchange server.