432 4.3.2 Microsoft bounce: recipient thread limit
What 432 4.3.2 means
The recipient mailbox is throttled because it is receiving too many messages too quickly, so delivery is deferred.
Message text
STOREDRV.Deliver; recipient thread limit exceeded
Common causes of 432 4.3.2
- Mailbox receives a burst of messages faster than its throttle allows
- Shared mailbox database throttling by design
How to fix 432 4.3.2
- Slow the send rate to that recipient and retry later.
- Check whether a bulk sender or automated system is flooding that mailbox.
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How to read 432 4.3.2
The first part, 432, is the SMTP reply code. Replies that start with 4 are temporary and replies that start with 5 are permanent (RFC 5321 §4.2.1).
The second part, 4.3.2, is an enhanced status code (RFC 3463 §2) written class.subject.detail. Class 4 is a Persistent transient failure (4xx): the command was not accepted, but the condition may clear, so the sender should try again later (RFC 5321 §4.2.1; RFC 3463 §2).. Subject 3 is mail system: a problem with the receiving system as a whole. The detail number refines the subject, and providers may define details of their own, which is why one code can read differently at Gmail, Microsoft and Yahoo.
Sending servers should retry a deferred message. RFC 5321 §4.5.4.1 advises waiting at least 30 minutes between attempts and trying for at least 4 to 5 days before giving up and returning a bounce. If the deferral keeps repeating, fix the cause rather than waiting.
Official source: learn.microsoft.com. Last verified 2026-10-20.
Related guides
- How to create an SPF record (syntax and examples)
- How DKIM works and how to publish a DKIM record
- How to set up a DMARC record, from p=none to p=reject
Related codes
- 4.4.7 Microsoft: message expired
- 4.7.26 Microsoft: ipv6 needs spf or dkim
- 4.5.3 Microsoft: too many recipients
FAQ
What does 432 4.3.2 mean?
The recipient mailbox is throttled because it is receiving too many messages too quickly, so delivery is deferred. This is a temporary failure.
How do I fix 432 4.3.2?
Slow the send rate to that recipient and retry later. Check whether a bulk sender or automated system is flooding that mailbox.
Is 432 4.3.2 permanent, and should I retry?
432 4.3.2 is a temporary failure. Your mail server normally retries by itself; if it keeps repeating, fix the cause.