Yahoo Inc is a division of the internet service provider Verizon Communications, headquartered in New York City. It's known for its freemail services AOL and Yahoo!. Yahoo Inc provides a detailed Postmaster page with contact options for investigating false-positive spam verdicts. Some senders may also qualify for their "Email Marketing Data Feeds" with detailed insight on performance in the inbox.
host xx.yahoodns.net [x.xx.xx.xx] SMTP error from remote mail server after MAIL FROM:<firstname.lastname@example.org> SIZE=2022: 553 5.7.1 [BL21] Connections will not be accepted from x.xx.xx.xx, because the ip is in Spamhaus's list; see http://postmaster.yahoo.com/550-bl23.html
host xx.yahoodns.net [x.xx.xx.xx] SMTP error from remote mail server after MAIL FROM:<email@example.com> SIZE=2022: 553 Mail from x.xx.xx.xx not allowed - 5.7.1 [BL23] Connections not accepted from IP addresses on Spamhaus XBL; see http://postmaster.yahoo.com/errors/550-bl23.html 
smtp;554 delivery error: dd This user doesn't have a example.com account (firstname.lastname@example.org) [-9] - example.yahoo.com
smtp;554 delivery error: dd Sorry, your message to email@example.com cannot be delivered. This mailbox is disabled (554.30). - example.yahoo.com
smtp;554 5.7.9 Message not accepted for policy reasons. See https://postmaster.yahooinc.com/error-codes
smtp;554 Message not allowed - [PH01] Email not accepted for policy reasons. Please visit https://postmaster.yahooinc.com/error-codes