If you're sending an e-invoice to an Estonian company and you're not sure if they can receive e-invoices, then you can check it from Estonian E-Business Register.

Just search using your customers business name and check whether they can or can't receive e-invoices.

If your customer can't receive e-invoices it is clearly stated under Receipt of invoices section:

If the customer can receive e-invoices it will be clearly stated under the same category (Receipt of e-invoices):

If you want to send e-invoices to a Finnish customer, then you can check it from verkkolaskuosoite.fi.