Will my email eventually get delivered?

A 4xx deferral means your server should retry automatically, and Yahoo may accept it on a later attempt once volume or pattern normalizes. But recurring TSS04 responses mean the underlying cause (reputation, complaints, volume) needs fixing, not just retrying.

Is TSS04 the same as being blacklisted?

No — it's Yahoo/AOL's own internal filtering signal, separate from third-party DNSBL blacklists. Check the blacklist checker separately if you want to rule those out too.

Yahoo / AOL

Yahoo/AOL TSS04 — temporarily deferred for reputation or complaints

[TSS04]

TSS04 is a Yahoo/AOL-specific deferral code (in the 4xx temporary-failure class) indicating the current sending pattern looks risky to their filtering systems — commonly due to unexpected sending volume, a rising complaint rate, or borderline domain/IP reputation. It's not a final rejection, but ignoring it repeatedly can escalate to harder blocking.

How to fix it

1
Reduce sending volume or rate
If volume recently spiked, scale back and ramp more gradually — Yahoo's filters weigh sudden changes heavily.
2
Check your complaint rate
High spam-complaint rates are a common trigger. Make unsubscribing easy and stop sending to unengaged addresses.
3
Verify authentication
Unauthenticated senders get less benefit of the doubt under load. Confirm SPF, DKIM, and DMARC with the compliance checker.
4
Check list quality
Remove hard bounces and long-unengaged addresses — a stale list drives both complaint rate and unexpected-pattern signals.

Meaning current as of 2026-07-14, cross-checked against the provider's own documentation. Providers do occasionally redefine codes — if this doesn't match what you're seeing, the source link is the authoritative reference.

How to fix it

Common questions