Setting up a sub domain on 123reg is technically not supported as I was told by their support team. However I did find out you can setup a full subdomain and even configure its own MX records as needed.
So lets say you have a domain and in our case its at2kf.co.uk and we have email setup on this domain info@at2kf.co.uk etc.
Lets say you now want to setup a subdomain for some reason, uksupport.at2fk.co.uk and you wanted to use email addresses @uksupport.at2kf.co.uk.
Well that’s actually no problem, let me show you how.
1. Login to 123reg.com and click on subdomains from the main menu.
2. Next type the name of the new subdomain and ensure you select the correct domain from the dropdown list.
Click ‘Add subdomain’.
3. Next click ‘Back to Main Menu’.
4. Now select your domain from the drop down menu and click ‘Manage’.
5. Click on ‘Manage DNS’.
6. Click on the ‘Advanced DNS’ tab at the top.
7. Now enter your new MX record as usual but for the DNS entry Hostname enter your subdomain. In our case its uksupport.
8. Now you can test that the new subdomain MX records are working by using a tool suck a mxtoolbox.com. Simply enter the full subdomain into the tool and click ‘MX Lookup’.
As you can see only one MX record was returned for this new subdomain which is exactly what we wanted.
Further down the image you can see I also did a check on at2kf.co.uk which returned its own MX records.
Haray! the subdomains DNS records are now working 😀
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