If the EMS Server is 8.6 (or 8.4), what is the minimum version of EMS client can I use?

[Reynaldo Libutan]

I understand that ideally we also use the same EMS client version as our EMS server.

But just in case we don't have access to other clients which means we can't upgrade them easily.

[Mark Mussett]

Generally older EMS clients are backward compatible with newer versions of EMS server. Any information regarding minimum version supported by EMS client will be documented within the release notes of the product.

I would recommend raising a support ticket with your exact version numbers.