My client has a .co.nz domain name, and now wishes to add a .com name - and it's available.

How is this going to work on their Office 365 account (all mail enabled users, some with mail and office suite subscriptions)?

Can I add this new domain into their Office 365 account? Or should I create a new Office 365 account. 

We just want to hook mail on this new .com domain.

For outbound mail , the users with newly created .com addys will need to be able to use Outlook, such that they can click 'From' and select either domains.

I'm unsure on how to proceed.

TIA,  Duncan.

Hi Duncan,

Based on my knowledge, what you required is possible. Please check if the following links help:

http://community.office365.com/en-us/f/155/t/195095.aspx

https://support.office.com/en-us/article/Can-I-add-custom-subdomains-or-multiple-domains-to-Office-365-5481401f-7771-490e-b728-b3a81305a32e

Since this forum focus more on Office Client side question, and your question is more related to Office 365, I'd recommend you post a new question in the Office 365 Community forum for further assistance:

http://community.office365.com/en-us/f/default.aspx

The reason why we recommend posting appropriately is you will get the most qualified pool of respondents, and other partners who read the forums regularly can either share their knowledge or learn from your interaction with us. Thank you for your understanding.

Steve Fan
TechNet Community Support