SMTP enhanced status code 4.4.2

What the registry says

The basic codes it travels with

• 421 <domain> Service not available, closing transmission channel

In practice

X.4.2 means the session was cut before the transaction finished. Gmail reports 451 4.4.2 for a timeout closing the connection. Common causes are slow sending clients, network problems and receivers that drop connections they consider suspicious. If it happens only with one provider and only at high volume, lower the number of parallel connections.

What the sender should do

Let the queue retry. Repeated 4.4.2 on one route points to network trouble or to the receiver dropping slow or unwelcome connections.

How providers use X.4.2

Quoted from each provider’s own error reference.

• Gmail 451 4.4.2

  Timeout - closing connection. For more information, go to About SMTP error messages.

Common questions

What does 4.4.2 mean?

X.4.2 means a connection was made but the transaction could not be finished, because of a timeout or a poor connection. It is a temporary error.

What should I do about 4.4.2?

Let the queue retry. Repeated 4.4.2 on one route points to network trouble or to the receiver dropping slow or unwelcome connections.

Would an email verifier have caught 4.4.2?

No. This reply is about your sending setup, the message or the receiving system, not about whether the address exists, so verifying the list will not prevent it.

Full guides for this code

• 451 4.4.2 — connection timed out