your message could not,be delivered to one or more recipients.

[Wouter Verhelst]

On Thu, Nov 16, 2017 at 04:22:30PM +0100, Peter Lebbing wrote:
> On 16/11/17 14:55, Jean-David Beyer wrote:
> > From where does it get port 451? My SMTP port is 465
> > 204.29.186.9 is my ISP for e-mail: AOL.
> 
> It's probably not a port. Note that the port 465 you are using to submit
> mail has nothing to do with how mail is delivered from there on. Port
> 465 is never used between mail servers[1].
> 
> It's probably SMTP status code 451, which is a temporary error message
> inviting the sending server to try again at a later time. Combined with
> the error message, I'm inclined to think it's a greylisting system on
> the receiving server. But apparently your ISP's mail server has given up
> on trying to deliver it and bounced it to you. Either your ISP is giving
> up too soon, or the receiving server is holding it off for too long. The
> latter might be because of a configuration error.

Alternatively, AOL might be trying to send the mail from a different
server every time. If the receiving server does implement graylisting,
then every time it sees a new IP address, sends it a 4xx status, and
waits for it to reappear. Only when it does reappear the IP address is
new, so it graylists again. Rince, repeat.

-- 
Could you people please use IRC like normal people?!?

  -- Amaya Rodrigo Sastre, trying to quiet down the buzz in the DebConf 2008
     Hacklab