Hi Procloud Nor,
Generally, Office 365 support the standard custom domain. In this situation, I recommend you go to the domain register to get more information about the standard.
In this issue, I understand the custom domain was accepted but the email didn’t work. If this is the case, I suggest you perform the following steps to narrow down this issue:
1. Go to Office 365 portal, click Domains to check if the custom domain was added correctly. If the status is verified, it indicate the domain was added correctly.
2. Change the custom domain with correct DNS record. Generally, the user need to change the name server of the custom domain to use Office 365 Online service. Please refer to http://onlinehelp.microsoft.com/en-us/office365-smallbusinesses/gg549203.aspx.
3. Refer to Troubleshoot issues after changing your domain name for additional information.
Thanks,
Eben Liu