But AT&T is being paid or has an agreement to operate the recipients' mailboxes.
TOS are gonna TOS, but if the small print reserves the right to block spam, or traffic from spammers, then proof of not being a spammer, or at least proof of a legitimate use, might create an obligation ATT has to its users to not block those addresses, even if there's no obligation to the 3rd party making the request.
The knowledge affects ATT's obligations to others, not the requestor.
Idk where that gets you in a practical sense, but its at least a line of reasoning that's beyond "ATT can block whatever it wants".
TOS are gonna TOS, but if the small print reserves the right to block spam, or traffic from spammers, then proof of not being a spammer, or at least proof of a legitimate use, might create an obligation ATT has to its users to not block those addresses, even if there's no obligation to the 3rd party making the request.
The knowledge affects ATT's obligations to others, not the requestor.
Idk where that gets you in a practical sense, but its at least a line of reasoning that's beyond "ATT can block whatever it wants".