Basic SMTP reply code · RFC 5321
432 Password transition needed
A reply to AUTH: the user must move to the chosen mechanism, usually by authenticating once with PLAIN (RFC 4954).
- Class: 4yz · Temporary failure
4yz: a transient failure. The command was not accepted, but may succeed if repeated; the sending server should try again (RFC 5321 §4.2.1). - Source
How 432 appears at providers
The exact text from the provider's documentation, as you see it in the bounce, and what it means.
Microsoft 365 / Exchange Online
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432 4.3.2
STOREDRV.Deliver; recipient thread limit exceeded
The recipient's mailbox is getting too many messages too quickly and is throttled for a while, so it does not affect others. The sending server retries.
Have the whole error message?
Sources: RFC 5321 · RFC 3463 · RFC 3464 · IANA · Gmail · Microsoft 365 · read on 26 September 2026