Question: all email services are based on which software model
[{'answer': 'the Simple Mail Transfer Protocol', 'provenance': [{'wikipedia_id': '9738', 'title': 'Email', 'start_paragraph_id': 14, 'start_character': 579, 'end_paragraph_id': 14, 'end_character': 612, 'bleu_score': 1.0, 'section': 'Section::::Origin.\n'}]}, {'provenance': [{'wikipedia_id': '9738', 'title': 'Email', 'start_paragraph_id': 71, 'start_character': 0, 'end_paragraph_id': 71, 'end_character': 433, 'bleu_score': 0.9716239638199891, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 11736974140432362697}, 'section': 'Section::::Servers and client applications.\n'}]}]