To configure your domain hosted on 123 Reg with SPF, you will have to add them to your SPF record.  The SPF mechanism used by 123 Reg is shown below.

mx a ip4:94.136.40.163
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If you are using 123 email, it should be:

mx a ip4:94.136.40.163 a:mailex.mailcore.me

For more information please click the button below.

You can configure your 123 Reg domain with DKIM via your 123 Reg Control Panel as described here:

Create a free OnDMARC account to test your configuration.