No Peer Certificate shows in diagnostics or Configuration failure log
Please browse to your server address (what you entered as the server address in the touchdown configuration) from the Internet browser on your device and see if you get a certificate error. Also, try browsing to the address from your PC and see if you also get a certificate error. If so, the SSL on your server is out of date or needs to be renewed.
If you are sure you are connecting to a secure site you can work around this by going to Touchdown settings>account and selecting Trust any server certificate. Most times you should not need to re-run Quick Configuration but if you find you still are not getting mail, make sure Fetch and Trust is selected and re-run quick configuration in Touchdown settings>advanced>legacy settings screen>account.