If you have the vendor center license I suppose that is a very cheap way - otherwise I would strongly recommend an external party - usually covering both in- and outbound einvoicing but with a portal for the smaller vendors (or customers) - Depending on number of vendors/customers etc it may be overkill but it is by far the superior solution, no change management needed when formats change and a smaller vendor becoming a bigger one can instantly be moved to einvoicing.
For Sweden there are a number of decent WAN providers, Pagero, Basware etc. - they both have global reach also but there are many other smaller/niché providers as well.