Locked Account/Domain/IP/Email-address details

Why did a message I sent get bounced, referring me to this page? has a number of different locks to avoid abuse of our systems. These include:

If you send a message to someone who has had their account locked, or from an external address, IP or other blocking characteristic, you will receive a delivery notification error like this:

I'm sorry to have to inform you that the message returned
below could not be delivered to one or more destinations.

For further assistance, please send mail to

If you do so, please include this problem report. You can
delete your own text from the message returned below.

The Postfix program host said: 554;
  Recipient address rejected: Account locked for abuse or overuse; see

You can work out what caused the block by looking at the response message