Just 0.3% of domains implemented an MTA-STS TXT record. 571 (19.5%) of these domains have implementation errors (see complete list below). Among the valid MTA-STS implementations, 54.3% publish an 'enforce' policy, while 45% have opted for a 'testing' policy. In summary, 1278 domains leverage MTA-STS to fortify their defenses against Man-in-the-Middle (MitM) downgrade attacks.