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

Wouter Verhelst w at
Thu Nov 16 17:56:34 CET 2017

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
> > 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

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