External mail client for answering cases

Been trying to convince the company to use the internal email feature, but with no luck. It is a requirement that an external mail client can be used to reply to support cases.
I have tried to configure the use of external mail client, but with no luck.

Ideally a mail would be created in the inbox after SuiteCRM parsed it, with the correct subject field e.g. [CASE:11]This is a support ticket
and with the body being intact as well as the sender.
This would enable the support team to just reply to that mail and have SuiteCRM parse the ‘Sent’ folder and update the case.

Don’t know if the above makes sense, but I would like to hear how other people use the Case module with external mail clients.

Thanks in advance,