Duplicate Emails with Email Security.cloud
Article ID: 161444
Updated On:
Products
Email Security.cloud
Issue/Introduction
You are seeing duplicate copies of an email being delivered to one of your users or a third-party reports recieving duplicates of an emails from your user.
Resolution
The table lists the most likely reasons that may cause duplicate emails.
Once you have established the nature of the problem, we can investigate if the duplication is occurring within our infrastructure.
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Cause
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Description
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Troubleshooting
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The email server is overloaded
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· If your email server is overloaded, you may need to set a limit to the amount of concurrent connections that the server accepts.
· If the email server response is slow. Connections requests are sent until the email server replies.
· If the server is set to do reverse DNS lookups before performing security checks, MessageLabs keeps sending the email again
· If the message size limits is set too low, the email server can either take too long to respond or it has reached its limit. In both cases, MessageLabs resends the email.
· You are subjected to a DOS/SPAM attack. A DOS/SPAM attack takes up all of your bandwidth, resulting in the inability to receive
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Check the available bandwidth, the email server capability and the number of connections to accept (50 is usually an acceptable number of connections.)
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Out of date CISCO PIX firewall
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It is a known issue. The CISCO software resets the connection if the "." and the email ending are in two different TCP packets.
The wildcard and the email ending in separate TCP packets does not match MessageLabs expected protocol
In this instance, MessageLabs resends the email.
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· Solution 1: Upgrade the PIX software
· Solution 2: Disable the SMTP fixup protocol in the CISCO PIX configuration so that our email servers can send emails to your email server instead of PIX acting as an intermediate relay.
Visit the CISCO website and search for CISCO defect number CSCds90792.
A patch exists for the PIX software, versions 5.2.4 and 5.2.5.
For newer PIX versions, we recommend that you disable "ESMTP Inspect".
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POP issues
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A POP server sets the email status to "downloaded" after emails have been downloaded. If the email retrieving process is interrupted, the email client restart downloading emails from the beginning
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Check connectivity
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Setup issues
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The server is not set up to delete emails from the server after download
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Check your server settings and ensure that it is set to delete emails after they have been downloaded.
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Multiple sending
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The sender has sent an email multiple times
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Select two duplicate emails randomly and check their message IDs
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Feedback
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