Complex sentence: Since the 1980s, many modern postal systems no longer overprint stamps for bulk purchases: bulk mail is franked using barcodes on pre-printed envelopes or on blank adhesive labels.
Split into simpler sentences: Since the 1980s, many modern postal systems no longer use overprints to indicate bulk purchases. Bulk mail is franked using barcodes on pre-printed envelopes or on blank adhesive labels.