Oops a server error occurred and your email was not sent (76997)

Yahoo Mail throws Oops, a server error occurred and your email was not sent, error 76997, whenever I try to send. Receiving works fine.

Web interface, happens on every send attempt. What causes 76997 specifically?

Error 76997 is a Yahoo Mail web interface error, and since it hits the browser based send specifically while receiving works, it is nearly always browser side state or a content trigger rather than an account problem. The fixes in order of hit rate:

1

Clear the browser's Yahoo state first, the most common cure: the error frequently comes from stale cached scripts or corrupt cookies for Yahoo. Clear cookies and cached data for the Yahoo domains, or test in a private or incognito window which ignores them, a successful send there confirming the cache as the culprit and pointing at a targeted clear.

2

Disable extensions, the second most common: ad blockers and privacy extensions interfere with Yahoo's send scripts, producing exactly this generic server error. Test with extensions off or in a fresh browser profile, then allowlist Yahoo in the offending extension.

3

Check the message content, the sneaky trigger: certain attachments, oversized ones or specific file types Yahoo blocks and occasionally specific content in the body, cause 76997 on send while a plain message sends fine. Test by sending a simple message with no attachment, and if that works, the previous attempt's attachment or content was the trigger, narrowing what to change.

4

Try another browser to isolate: sending fine in a different browser while the usual one fails after clearing cache and extensions points at a deeper profile problem in the original browser, worth a profile rebuild, while failing in every browser moves suspicion to the account or Yahoo's service, checked against Yahoo's status.

When it fails across all browsers and devices after these steps, the residue is account or service side, a temporary Yahoo issue that clears on its own or occasionally an account flagged for a sending review, where Yahoo's help channels become the path. But the overwhelming majority of 76997 reports resolve at step one or two, the browser state and extensions, since a receiving account with a web only send failure is almost definitionally a browser side problem.

Private window sent fine so it was cache, cleared the Yahoo cookies and normal sending returned. Weeks of not being able to send from my main browser fixed in five minutes. The receiving works means browser side logic is the useful principle here.