RPC detected an integrity violation while decrypting an incoming message

Hello everyone,

We have an issue in one of our offices, there are 12 users with identical Outlook setups.

5 of these 12 suddenly started having severe problems with Outlook constantly disconnecting and reconnecting, failing to correctly synchronize folders and failing to send messages. The event log on the client PC didn't reflect anything useful and the only thing we could find on the Exchange server was this error in the Security log:

4816: RPC detected an integrity violation while decrypting an incoming message

RPC requirement is set to False on the server (this is a default setting in Exchange SP1). But Outlook by default encrypts messages so it appears that the Exchange is failing to decrypt these messages. The error message goes on to provide a source IP address for the problem and these all match the specific users with the issue.

Unticking encryption in the affected Outlook profiles is a workaround for the issue, but obviously as many other users are set by default to encrypt, we need to fix the root issue of the Exchange failing to decrypt to prevent issues popping up in future.

We have searched high and low on Google with little mention of this issue.

We are running Exchange SP1 on Server 2008 R2. Client PCs are Windows 7 and Outlook 2010.

Any help would be appreciated.
AucklandAsked:
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Simon Butler (Sembee)Connect With a Mentor ConsultantCommented:
I would start by updating Exchange.
Exchange 2010 SP1 is no longer supported, you need to be on SP2 or preferably SP3.

As it is remote people my instinct is firewall. That can break the encryption in my experience.

Simon.
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AucklandAuthor Commented:
Thanks Simon, we will update Exchange and see if that resolves it.

It is a remote office but with a local Exchange server, should've specified that sorry.

I'll report back once we have applied updates, thanks very much for the suggestion.
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AucklandAuthor Commented:
Updated all Exchanges to SP3, still have the same issue.

When users are set to unencrypted, attachments either do not send at all or arrive in a corrupted form (JPGs arrive with distorted colours, PDFs corrupt and Excel documents arrive corrupted).

When users are set to use encrypted mode, Exchange repeatedly shows as Reconnecting, Online, Reconnecting, Online etc (in 5 second intervals) and items stick in the Outbox due to this. Incoming mail appears to work but arrives in batches presumably due to the intermittent connection.
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Simon Butler (Sembee)ConsultantCommented:
Have you checked the network card driver is at the latest version?
Run BPA from the toolbox to confirm there is nothing else wrong?

What else is on the server? Does the AV have the correct exclusions in place?

Simon.
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