554 validating sender
If this is enabled, the router will sometimes intercept SMTP traffic and replace data in it before it reaches h Mail Server which will cause problems.
If a SMTP client authenticates but the username or password is incorrect, or the account is disabled, h Mail Server sends this error message to the client.
This error message is issued if the domain address given in the HELO command does not have the correct syntax.
If a SMTP client tries to use the TURN command h Mail Server responds with this error code.
For information on how to enable SMTP authentication, check the HOWTO.
You have enabled SMTP authentication for the IP range that the user is connecting from, but the user has not configured his client to use SMTP authentication. Either configure your email client to use SMTP authentication.
After a SMTP client has connected to a SMTP server, the first thing it should do is to identify itself using the HELO or EHLO command.
If the client does not do this, h Mail Server responds with this error message.
As an example, the default IP range configuration does not allow external users to send messages to other external users.
This is to prevent people from using your server to send spam.
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This error message is issued if grey listing is enabled, and the sender, recipient and IP address triplet does not match an existing greylisting triplet.