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swgit
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Exchange 2010 - Mails stuck in queue with 451 error

Hello Experts,

I'm having a couple of e-mails stuck in the queue with error "451 Requested action not taken because the message failed RFC compliancy checks."  This is for one particular domain only, not the rest.

Please advise.  Thanks.
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Manpreet SIngh Khatra

8/22/2022 - Mon
Manpreet SIngh Khatra

Check if that Domain is not blacklisted www.mxtoolbox.com as it seems some issues at their end

- Rancy
swgit

ASKER
nothing on blacklist.  their smtp's show "Warning - Does not support TLS." and "5.522 seconds - Warning on Transaction Time" on their mx records.
Manpreet SIngh Khatra

Are you able to do Telnet as it could be that either their MX or some Firewall issues

- Rancy
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William Peck
swgit

ASKER
I did telnet but the connected session went to a total different domain.
Manpreet SIngh Khatra

What .... seems something wrong or they have some changes so better check with the Recipient Admin

- Rancy
swgit

ASKER
Could this be something on my end too?  i.e. configurations of the Receive Connectors under Hub Transport?  What would be the recommendations for the Default and Client connectors' Authentication?
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Manpreet SIngh Khatra

Is this happening for many or just one domain ?

- Rancy
swgit

ASKER
just that one single domain.
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Manpreet SIngh Khatra

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swgit

ASKER
Receiving end is looking into the problem.  Thanks, Rancy, as always!
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James Murphy
swgit

ASKER
Just to follow up with this - Receiving end whitelisted our domain on their spam-filter appliance and e-mails to that domain working normally again.  They still haven't told us what was considered out of RFC specs from our e-mails.  I'll let you know more if/when I hear from them on that.  Thanks, again.
Manpreet SIngh Khatra

As usual Whitelisting or Appliance upgrade or some configuration changes messup things .... i too would like to know more on this

- Rancy