I am searching for an E-mail client that can connect all my emails through my domain and is able to add a reference number to all incoming and outgoing mails for all the accounts, is that possible in any way ?.
with eM Client you can set up all your email accounts. They will be treated as separate accounts, but you can set up forwarding to connect them or just use Smart folders that collect all your data together (ie All Inbox folder, All Unread, Flagged, etc.).
We don’t have any function to add reference numbers, but you can use categories (and even assign those automatically using Rules).
I am not sure what other features you’d need/expect, but if you download eM Client, you will be able to run a DEMO version for 30 days with no limits.
If you like eM Client, you will then need to register either for a FREE or PRO license, so maybe just give it a try first and see if it fits your needs.