Yahoo Deferral Codes TS01, TS02, TS03, TSS04, TSS05 and TSS09

Yahoo's TS and TSS codes are deferrals: Yahoo is refusing your mail for now, usually because of user complaints, an unexpected jump in volume, or a poor reputation on your sending IP. Most of them (TS01, TS02, TSS04, TSS05) are temporary 421 responses, so your server keeps retrying and mail eventually gets through once the pressure eases. TSS09 and the "permanently deferred" variants are different: Yahoo has stopped accepting mail from that IP, and retrying won't help until you fix the cause.

The same codes apply to AOL, which runs on Yahoo's mail platform.

What the bounce says

The temporary versions look like this:

421 4.7.0 [TSS04] Messages from 203.0.113.7 temporarily deferred due to
unexpected volume or user complaints - 4.16.55.1; see
https://postmaster.yahooinc.com/error-codes

421 4.7.0 [TSS05] Messages from 203.0.113.7 temporarily deferred due to
unexpected volume or user complaints - 4.16.55.1

421 4.7.0 [TS01] Messages from 203.0.113.7 temporarily deferred due to
user complaints

421 4.7.0 [TS02] Messages from 203.0.113.7 temporarily deferred due to
user complaints - 4.16.56.1

The permanent versions:

421 4.7.1 [TS03] All messages from 203.0.113.7 permanently deferred

553 5.7.2 [TSS09] All messages from 203.0.113.7 will be permanently
deferred; Retrying will NOT succeed.

The exact wording and the trailing diagnostic number vary between bounces. What matters is the code in brackets, the IP it names, and whether it says "temporarily" or "permanently."

What it means

Yahoo's SMTP error page groups all of these under "Message temporarily deferred (e.g. TS* Errors)" and lists four possible causes:

• Substantial complaints from Yahoo users
• Objectionable content or spam-like characteristics
• Poor reputation of the sending IP
• Unusual traffic patterns from your mail servers

Yahoo doesn't publish what distinguishes TS01 from TSS04 or TSS05, so treat the text of the bounce as the real signal. "User complaints" points at your complaint rate. "Unexpected volume or user complaints" means either one could be the trigger. "Permanently deferred" means the IP is blocked outright.

Note the IP in the bounce. These are IP-level decisions. If you send from several IPs and only one is deferred, the problem is likely tied to whatever traffic that IP carries.

Common causes, most likely first

1. A complaint spike. Yahoo requires a spam rate below 0.3%, measured against mail delivered to the inbox. One send to an old or cold segment can push you past it.
2. A volume jump. A new IP sending at full volume, or a big seasonal campaign on top of your normal traffic, reads as unusual traffic.
3. Shared IP reputation. On a shared ESP pool, someone else's bad send can defer yours. Yahoo's own advice for complaint problems includes considering a dedicated IP if you share one.
4. List quality. High unknown-user rates and spam trap hits drag down IP reputation and feed the complaint problem.
5. A compromised server. If you run your own MTA and don't send bulk mail, Yahoo suggests checking your outbound queues for spam you didn't send.

How to fix it

1. Find which IPs and streams are deferred. Pull 421 and 553 responses from your logs for Yahoo and AOL domains, grouped by sending IP and campaign.
2. Check your complaint rate. Enroll your DKIM domain in Yahoo's Complaint Feedback Loop through Sender Hub and activate Insights for a per-domain complaint rate. Suppress every complainer.
3. Pause the likely trigger. If one campaign or list source lines up with the start of the deferrals, stop it.
4. Slow your send rate to Yahoo. Lower connections and messages per hour for Yahoo and AOL domains and ramp back up over several days.
5. Clean the list. Remove hard bounces and long-unengaged addresses. If you can't say where an address came from, don't mail it.
6. Confirm authentication. Bulk senders need SPF, DKIM and a passing DMARC record, plus one-click unsubscribe. Check with the email checker.
7. Let retries happen. Don't resend deferred mail manually. Your MTA retries 4xx responses on its own; resending just adds volume.
8. Open a ticket if it persists. For TSS09, or a TS deferral that continues over an extended period after you've fixed the cause, open a ticket from the Sender Hub contact page. Include the exact error text, the diagnostic codes, timestamps and sending IPs.

How to confirm it's fixed

Deferral counts for Yahoo domains should fall in your MTA logs, and mail that was queued should start delivering on retry. Watch your complaint rate in Insights for at least a week. A seed test will show whether accepted mail lands in the inbox or the spam folder, since acceptance and placement aren't the same thing.

How to keep it from coming back

Keep the feedback loop active, track complaint rate per campaign rather than per month, and warm up any new IP or new audience gradually. The broader playbook is on why Yahoo and AOL block email.

When to get help

If deferrals keep returning after you've cut volume and cleaned your lists, or you're stuck on a TSS09 block, an outside look at your data usually finds the stream that's causing it. Get in touch.

FAQ

Is TSS04 a blocklisting?

Not in the public DNSBL sense. It's Yahoo's internal system deferring your IP. You can't look it up on a blocklist checker; it only shows up in your bounces.

Will my deferred emails eventually be delivered?

Usually, for 421 codes. Your server retries them, and many get through on a later attempt. Mail that sits in the queue past your MTA's retry limit will bounce for good, commonly after several days.

What's the difference between TSS04 and TSS09?

TSS04 is a temporary 421 deferral and your server should keep trying. TSS09 is a 553 permanent response that says retrying will not succeed, so you need to fix the cause and contact Yahoo.

Does warming up a new IP prevent TS deferrals?

It helps a lot. Yahoo's guidance for new IPs is to increase volume gradually and only send to people who asked for your mail.