How do I get recipient to see/reply to a different sender email address from the one I'm sending from?

My account is set to send through my ISP’s email address (xyz@ISP.com) but when clients reply (or hover mouse over my sender name) I want them to reply to/see my personal email address  (john@johnsmith.com). 

I already have forwarding set up from john@johnsmith.com to xyz@ISP.com so that is sorted. 
I could do it easy through Windows Live Mail but how do I do this with EM Client ?

It’s a marketing issue - it looks much more professional.

eM Client does not have the option to specify a different reply to address as in some other email clients.

The best option is to setup and use the john@johnsmith.com email account in eM Client, and cancel the forwarding from that account to xyz@ISP.com.

Aliases are also an option, but usually don’t work where the domains are different.

You can also specify a different email address in your account settings under User Information. Some email providers do not allow relaying, so it may not work.