Microsoft Exchange can host email for several domains. Many companies take advantage of this. For example, they may have a domain for their parent company and individual domains for each separate company or product. So the company could use a single Exchange server to get email for PARENTCOMPANY.COM, SUBCOMPANY1.COM, SUBCOMPANY2.COM, PRODUCTNAME1.COM and so on.
This is completely transparent for the end user, and that’s usually a good thing. However, if someone is getting emails from all Exchange domains, there’s no easy way for them to tell which domain the email was originally sent to. Let’s say that Bob works for ABC Company. ABC Company is the parent company of TUV Company and XZY Company. Bob has email addresses in the form of Bob@ABCCompany.com, Bob@TUVCompany.com and Bob@XYZCompany.com. The Exchange server will deliver email addressed to any of those addresses to Bob’s Exchange mailbox… but Bob won’t easily be able to tell which address the email was originally sent to. If Bob tries to create an Outlook rule to “move email with ‘Bob@XYZCompany.com’ in the recipient’s address” to a folder in his inbox, the rule will fail, because Exchange treats all SMTP addresses equally.
However, if Bob enters each email address into a separate rule that searches for the address as “specific words in the message header” the rule will work. This is because Outlook will scan the actual headers of each email for “Bob@ABCCompany.com”, “Bob@TUVCompany.com” and\or “Bob@XYZCompany.com”. Bob can then have Outlook move the email to “ABCCompany.com” “TUVCompany.com” or “XVZCompany.com” folders in his Inbox, or perform any number of other notifications.
This is not new knowledge or anything. For some reason, Microsoft has never made this explicitly clear to anyone, and there are tons of posts on Internet message boards looking for a solution to this very problem. Since Microsoft couldn’t be bothered to explain this clearly in Outlook (or simply make the “move email with ‘Bob@XYZCompany.com’ in the recipient’s address” rule work with Exchange SMTP addresses), this question comes up somewhat often.