In late crm 4, email address resolution behavior was changed. In earlier versions, if you had an e-mail address on multiple records (account, contact, lead, user), it would only resolve to one of them. This behavior was changed so that if there are multiple records with the same address, when an e-mail comes in with that address as a recipient, CRM will resolve to all of the records with that address, creating multiple activity parties.
Some implementations have duplicate email addresses by design, and this multiple resolution can cause problems in some situations, such as confusing users when they see 10+ recipient activity parties for the same address, and can cause emails to get linked to the wrong records.
Please add additional system settings to make CRM work better in these scenarios. Additional options that would be good:
Ability to turn off email address resolution
Ability to turn off email address resolution to inactive records
Ability to select (control) record types for email address resolution
option for Track None for incoming mail