Can I use Dotpost if I don't have a UK address?

Yes, it is possible to use Dotpost if you do not have a UK address. 

When a sender invites you to use Dotpost they will send the activation code to your address even if this is non-UK. You can use this to Register or Add New Sender.

Delete

Make sure you select No Postcode and enter the address exactly as it appears on your invitation letter.