4.4.3

Delayed Message: network issue with the receiving system

The email message has not yet been delivered because a network problem prevented the recipient's email provider from delivering the message.

Fixes

The sender's email system 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.

4.4.3: Official Definition

4.X.X

[RFC3463] (Standards Track) from the The Internet Engineering Task Force (IETF) definition for codes that start with 4.X.X:

A persistent transient failure is one in which the message as sent is valid, but persistence of some temporary condition has caused abandonment or delay of attempts to send the message. If this code accompanies a delivery failure report, sending in the future may be successful.

X.X.3

[RFC3463] (Standards Track) from the The Internet Engineering Task Force (IETF) definition for codes that end with X.X.3:

The network system was unable to forward the message, because a directory server was unavailable. This is useful only as a persistent transient error. The inability to connect to an Internet DNS server is one example of the directory server failure error.