Our organization uses Exchange 2010 SP1 RO 6.
One of our users cannot receive mails sent from an external email address when the mail has a 15 MB attachment (the user can receive mails from the same sender when the attachment size is less than 10 MB), although our Exchange server is set with mail size receive limits as 20 MB.
All our mails come through an external spam scanner ZScaler. But these mails with a 15 MB attachment do not appear in the logs of the spam scanner nor in the Exchange server logs.
The sender receives this error reply, after trying to send a mail to our user.
The following organisation rejected the message: mta1c.mail.zscaler.net.
Diagnose information for system administrator:
Generating server: TM-SE-EX.Myhrvold.local
mta1c.mail.zscaler.net #554-Transaction failed (id=4F74675610C00001), maximum 8 recipients listed below: 554-Address: <firstname.lastname@example.org> Server:18.104.22.168 Command:EODT Error:554 Transaction failed 554 Transaction failed ##
22.214.171.124 is incidentally ‘mta1d.mail.zscaler.net’ which is not located on our MX records.
Our MX records are as:
The receive limit for that particular user’s mailbox is not set.
All receive connectors have a maximum receive limit of 20 MB.
Maximum receive size for Organisation (Global Settings->Transport Settings) is also 20 MB.
These blocked mails, do not appear in the logs of the Spam scanner and neither in our Exchange Transport logs.
Our spam scanner, ZScaler, says that the mail is blocked by our Exchange server and not the spam scanner.
Where could the problem lie?