5.4.2

Message Not Delivered: network connection timed out

The message could not be delivered because the sender's email provider and the recipient's email providers got disconnected before the message had been handed over for delivery.

Fixes

The sender's email program will retry this message a few more times and provide further updates.

If the sender is not notified within a few days that the message was delivered, try sending it again. Or contact the recipient another way, such as phone or text message.

5.4.2: Official Definition

5.X.X

[RFC3463] (Standards Track) from the The Internet Engineering Task Force (IETF) definition for codes that start with 5.X.X:

A permanent failure is one which is not likely to be resolved by resending the message in the current form. Some change to the message or the destination must be made for successful delivery.

X.X.2

[RFC3463] (Standards Track) from the The Internet Engineering Task Force (IETF) definition for codes that end with X.X.2:

The outbound connection was established, but was unable to complete the message transaction, either because of time-out, or inadequate connection quality. This is useful only as a persistent transient error.