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Exchange 2010 sending e-mail - 450 4.7.1 Client host rejected: cannot find your hostname

Hi,
We recently replaced our internet connection.

When we send e-mail to specific external domains we get this error:
 450 4.7.1 Client host rejected: cannot find your hostname, [MyExternalIP]

according to google I need to set the PTR record so that a reverse dns for [MyExternalIP] would return "mail.[mydomain]". So I contacted my provider yesterday and they now have set it. I can even test it with online tools and it now returns "mail.[mydomain]".

It has been almost 24 hours now since the change and I still see this error in exchange queue viewer for atleast 2 external domains.

some facts:
- other domains do accept our mails.
- my SPF record is correct and google says SPF pass.
- My exchange server uses "mail.[mydomain]" to say HELO or EHLO.
- I do have some internal DNS issues but that couldn't be the case because the receiving mail server (a different company) will never use my DNS.
- the mails dont bounce immediately, my exchange will keep trying and I can tell the queue to retry. I did this several times.
- I also restarted Exchange and emptied the queue and tried mailing again.

should I just wait longer or is there something else I can do or check?

kind regard,
Ramon.
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Sul05
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I now seem to be able to send mails to a domain that I previously couldn't. some others still not working. But I'm quite sure you are right and that it just needs some time.
Thank you for your response.