>> per SMTP destination multiplied by N number of destinations
The number of people using anything other than google, apple, microsoft or yahoo for personal email these days is vanishingly small; and of the remainder, almost all of them are on major broadband providers. If you were some local ISP blocking us, that wouldn't be worth the trouble of sending a legal letter. I'd just tell that particular customer to contact you and ask why you weren't delivering our mail.
This only leaves other corporations that provide their own mail services to people who work there, and if those people want to get their mail they can call IT.
The number of people using anything other than google, apple, microsoft or yahoo for personal email these days is vanishingly small; and of the remainder, almost all of them are on major broadband providers. If you were some local ISP blocking us, that wouldn't be worth the trouble of sending a legal letter. I'd just tell that particular customer to contact you and ask why you weren't delivering our mail.
This only leaves other corporations that provide their own mail services to people who work there, and if those people want to get their mail they can call IT.