Yahoo Inc

4.0.0

Yahoo is not accepting mail on this connection right now. Treat it as temporary and retry with backoff.

4.0.0-2

Yahoo closed the connection after hitting the max messages per connection. Send fewer messages per SMTP session and retry.

4.7.0

Yahoo deferred this for volume spikes, complaints, or weak reputation. Check complaint and bounce rates, then slow sending until it clears.

4.0.0

This Yahoo inbox is receiving mail too quickly. Wait and retry at a lower rate to that address.

4.0.0

Yahoo hit a temporary resource limit while accepting mail. Retry with backoff. It usually succeeds on a later attempt.

4.0.0-2

Yahoo reported an internal server error. Retry with backoff. Escalate only if it stays stuck.

4.0.0

Yahoo reported a temporary domain failure. Retry with backoff. Investigate if the same domain keeps failing.

5.0.0

Yahoo rejected the SMTP command for bad syntax. Fix envelope or header formatting, then retry.

5.0.0

Yahoo denied relaying for this address. Authenticate properly and send only to accepted recipients.

5.1.1

Yahoo aborted delivery and the mailbox was not found. Treat it as a hard bounce and remove the address.

5.7.1

Yahoo blocked your IP because it appears on Spamhaus. Delist with Spamhaus, then retry after caches refresh.

5.7.1-2

Yahoo blocked your IP because it appears on the Spamhaus XBL. Delist with Spamhaus, then retry after caches refresh.

5.5.4

Yahoo says this user does not have an account at that domain. Treat it as a hard bounce and remove the address.

5.5.4-1

Yahoo says this mailbox is disabled, often an account used only for login elsewhere. Suppress the address.

5.5.4-2

Yahoo aborted the requested mail action. Verify the address and content. Suppress it if the same abort keeps repeating.

5.7.9

Yahoo rejected this for policy reasons. Review content, authentication, and complaint rates before sending again.

5.5.4-3

Yahoo rejected this on phishing suspicion. Review URLs and images. Request a review from Yahoo postmaster only after the content is clean.

5.5.4-4

Yahoo rejected the message because headers are not RFC compliant. Fix header formatting, then resend.

5.5.4-5

Yahoo rejected the message for a policy rule. Review content and authentication, then retry carefully.

5.5.4-6

Yahoo says this address is no longer valid. Treat it as a hard bounce and remove it.