The option to use a custom domain name with Office 365 is only available for Office business packages.
To map your Namecheap domain with an Office 365 account, you'll need to do the following:
1.
Sign in to your
Namecheap account.
2. Select Domain List from the left sidebar and click on the Manage button in front of your domain name:

3. Go to the Advanced DNS tab and click on the Add New Record button:

4. Here you will need to make the necessary changes in the Host Records and Mail Settings sections.
In the Host Records section, you will need to add the following ones:
Type | Host | Value |
CNAME Record
| autodiscover | autodiscover.outlook.com |
CNAME Record
|
sip | sipdir.online.lync.com |
CNAME Record
| lyncdiscover | webdir.online.lync.com |
CNAME Record
| msoid | clientconfig.microsoftonline-p.net |
CNAME Record
| enterpriseregistration | enterpriseregistration.windows.net |
CNAME Record
| enterpriseenrollment | enterpriseenrollment-s.manage.microsoft.com
|
TXT Record
| @ | TXT Value generated for your domain in the Office 365 account*
|
TXT Record
| @ | v=spf1 include:spf.protection.outlook.com -all
|
Type | Service | Protocol | Priority | Weight | Port | Target |
SRV Record
| _sip
| _tls
| 100
| 1
| 443
| sipdir.online.lync.com
|
SRV Record
| _sipfederationtls
| _tcp
| 100
| 1
| 5061
| sipfed.online.lync.com
|
This is how your records should look like:
In the Mail Settings section, select the Custom MX option and create the record for @ Host pointing to [yourdomain-tld].mail.protection.outlook.com with 0 Priority:
Once you've done so, press Save All Changes in both sections.
Give it some time and a few tries to pick up the change.
That's it!
If you have any questions, feel free to contact our Support Team.