Rickles:

 

Update:  Checked Gmail Settings thoroughly, and all states that my Reply-to address is different to my Gmail one … excellent.

 

IF I create and send an email using browser/web-based Gmail, then the recipient will get the desired 'other' address when clicking on Reply … again all good.

 

What fails, however, is if I send an email using Outlook through Gmail, the recipient only sees the Gmail address when clicking Reply. 

Ah I can see where the issue is. You are assuming that Google and Microsoft want to play nicely together... 😐

     >Ah I can see where the issue is. You are assuming that Google and Microsoft want to play nicely together... 😐<

I think this may the case because when using another email client, it all worked perfectly!