ExDox by United Data delivers your invoices (sales or purchase) electronically - no printing, no paper, no envelopes, no postage.

It probably links direct to your accounts package (and if it doesn't we can develop an interface).

There is not thousands of pounds of software to buy.  There is no complicated integration to go through.  Everything that is needed is on probably on a single CD.

In addition once a document is delivered you get notification so your customer cannot claim they haven't got your invoice and there is full tracability in the event of a dispute.