Some Mail Servers are now only accepting TLS 1.1/1.2 connections when connecting using SSL, if this is the case you may receive an error similar to this within Outlook: Server doesn't support the connection encryption type.
If you believe this to be the issue you can run the mail server through this Qualys scan: https://www.ssllabs.com/ssltest/index.html
If TLS 1.1 and/or 1.2 are the only supported protocols and you're running Windows 7 you will need to make sure that Service Pack 1 is installed and then install following two updates;
- http://catalog.update.microsoft.com/v7/site/search.aspx?q=kb3140245
- https://support.microsoft.com/en-us/help/3140245/update-to-enable-tls-1-1-and-tls-1-2-as-a-default-secure-protocols-in
Reboot if required and then run the attached Reg Key to enable TLS 1.1/1.2 on Windows 7, alternatively the Reg keys are pasted below;
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.1\Client]
"DisabledByDefault"=dword:00000000
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.1\Server]
"DisabledByDefault"=dword:00000000
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Client]
"DisabledByDefault"=dword:00000000
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2\Server]
"DisabledByDefault"=dword:00000000
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