In the Inbox of a user encountering this issue, review the Internet headers of the message. Are there more than one occurrence of the Subject header? This may cause the Outlook mail client to become confused.

If there is only one Subject header line in the Internet headers and it's correctly formatted, then for whatever reason, the Outlook mailclient and Outlook Web Access is not rendering it correctly.

Can you possibly provide some samples of the internet headers?

We prepend the subject of positively identified spam with [SPAM+] and have been doing so for years.  Each user has a rule setup that moves anything with [SPAM+] to their 'Junk E-mail' folder.  This system has worked well for years.

About 2 months ago, we started seeing messages with the subject truncated after [SPAM, which means the message sits in the inbox instead of being processed by the rule mentioned above.  This has been pretty random but it almost seems like it's affecting the same people over and over again.... randomly.

What's really strange is the header shows the correct subject line with the properly applied spam tag.  The subject is also truncated when the message is viewed in Webmail.  I created a new rule [SPAM++] for a user that was seeing this once a week.  He continues to see it.  Lastly, I created yet another rule for said user [JUNK+] a few days ago and am still waiting for results.

This is acting like an Exchange/Outlook problem but I can't figure out what would cause this.

Your thoughts and comments are GREATLY appreciated!