Salesforce for Outlook (SFO) Sync Fails — Required Fields Are Missing: [LastName] Error

This article explains how to resolve the Salesforce for Outlook (SFO) sync error "Required fields are missing: [LastName]". This error occurs because Salesforce requires a Last Name value on all Contact records. Contacts synced from Outlook that are missing a Last Name will fail to sync to Salesforce.
Steps to Resolve

1. Double-click the SFO system tray icon to open the error dialog with the full error details.
2. If the error message reads "Required fields are missing: [LastName]", proceed with the steps below.
3. Click on the Contact name displayed in the SFO error screen. The name appears as a hyperlink that opens the Contact's detail page directly in Outlook.
4. Click on Full Name.
5. The Check Full Name window opens.
6. Update the Last Name field. Last Name is a mandatory field in Salesforce. If the contact does not have a Last Name, or if you are syncing a company record as a contact, you may use a placeholder such as a dot ( . ) or comma ( , ) to satisfy the field requirement.
7. Click OK, then click Save & Close.
8. If you have more than one Contact with a missing Last Name, repeat steps 3–7 for each affected Contact.
9. On the SFO error screen, click Retry. If you have already closed the error screen, right-click the SFO system tray icon and select Sync > Sync Now.
10. The sync should complete successfully and the error message should no longer appear.