Company had recently changed e-mail addresses company wide to a new suffix. Example:
MyName@OldComanyName.com
to
MyName@NewCompanyName.com
Aliases were setup on their e-mail server to forward any e-mails sent to the old address to the new e-mail addresses.
Stat was setup with the old e-mail addresses for most users.
The e-mails went out as the old address and were received by the Stat users because of the alias, but when they replied, it was from the new e-mail address and Stat did not recognize this e-mail address as the same person.
Change the e-mail address for all Stat users to the current e-mail address, not an alias or mapped address.
Go to: User Options -> User Maintenance
Edit the Email Address field to the correct current e-mail address for each user.