Why are emails missing from the BusyContacts Activity List?
To show email activity, select a contact whose card contains the email address used in the messages, show the Activity List, and enable the relevant Mail categories in its Activity menu.
The next check depends on the mail app that supplies the messages.
Apple Mail on current macOS versions
Use BusyContacts Mail Assistant, the Apple Mail extension. Follow Adding Mail to enable capture in BusyContacts and the extension in Apple Mail.
Then open a message from or to the selected contact in Apple Mail and return to BusyContacts. The extension captures messages as Mail makes them available. It cannot automatically import your entire mail history, so downloading a mailbox alone does not make all its messages appear.
MailMate and other email apps
MailMate needs Spotlight indexing enabled and an accessible messages folder. Follow MailMate setup.
For MailMaven, Outlook, Spark, Thunderbird, and other clients, see email app compatibility. Choosing a default email app does not enable its message history in the Activity List.
Older macOS versions
Older instructions for Mojave and Catalina relied on Apple Mail's Spotlight data or the legacy BusyContacts Mail plug-in. That plug-in is no longer supported. Rebuilding Spotlight or trying to reinstall the plug-in does not enable the current Apple Mail integration.
Use a supported macOS and BusyContacts version with Mail Assistant. If you need help with an older Mac, contact support and include your macOS and BusyContacts versions.