450 Requested mail action not taken: mailbox unavailable

The mailbox cannot be used right now, for example because it is busy or locked. It is a temporary failure.

450 Requested mail action not taken: mailbox unavailable

Temporary: it may work if you retry

The mailbox cannot be used right now, for example because it is busy or locked. It is a temporary failure.

Usual causes

The mailbox is temporarily locked or busy.
The receiving server is using greylisting: it refuses the first attempt from a sender it does not know and accepts a retry a few minutes later.
A policy is delaying mail from your sending address.

What to do

Retry later. Greylisting clears on its own, usually within minutes.
If the text mentions a policy or reputation, see the 4.7.x entries and check your SPF, DKIM and DMARC.

Usually the fault of: receiving server.

Common questions.

What does 450 mean?

The mailbox cannot be used right now, for example because it is busy or locked. It is a temporary failure.

Will retrying fix 450?

Often yes. It is a temporary failure, and mail systems retry for you. If it keeps failing for days, look at the causes listed above.

How do I fix 450?

Retry later. Greylisting clears on its own, usually within minutes. If the text mentions a policy or reputation, see the 4.7.x entries and check your SPF, DKIM and DMARC.

Other codes: 250 · 421 · 451 · 452 · 500 · 501 · 503 · 530 · Decode a whole bounce message

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