I am testing Zoho One, and have found that the Licensing for Mail does not allow aliases or multiple domains to be used. These features are available in the stand-alone Zoho Mail program. The problem with this is that you cannot use this with the lower license price for One. 

So, has anyone used an external mail server (such as Office 365) which allows these features, then have this forward to Zoho One, which would then forward out to the Office 365 server. I guess this is similar to how many mail scanning applications work. This just does not seem very clean, but the cost of Office 365 for mail is small compared to the additional $60 per license for Zoho to add this feature (once you go to the more expensive One license plus the Per user stand-alone Mail license).

i am interested in understanding how people do this in practice. 

Thank You in advance,

Bryan Evans