ContactFix is an AddIn for Outlook 2013 that fixes a serious bug with Google Apps Sync. You can see the status of the bug on Google’s KNOWN ISSUES page but an exerpt is included below;

Messages sent to contacts in Outlook 2013 are not delivered to selected contacts
Status: Outlook 2013 users who are using Google Apps Sync for Microsoft Outlook® may notice that some of their sent messages are not being received and appear to be missing recipients in the ‘To:’ field of any affected message headers. This behavior is caused by using the ‘Add to Outlook Contacts’ option in Outlook 2013.

If you’re experiencing this behavior, you’ll most probably see multiple instances of the following error in your Google Apps Sync logs:

Can’t determine recipient email: ’3002001f:SMTP’ ’39fe001f:(null)’ ’3003001f:undisclosed-recipient

This is a major problem with Google Apps Sync and Outlook 2013. For Outlook users, the email appears in the sent items and it looks like it sent OK, but the recipient will never receive the email. ContactFix scans through all your contacts and identifies any broken ones, then repairs them. It also tracks you as you add new contacts and prevents them from breaking on the fly.

You can purchase a license today to protect yourself from broken contacts.