Problem with Zoho CRM syncing sent/received emails to Leads

Problem with Zoho CRM syncing sent/received emails to Leads

We currently use Zoho CRM + Zoho Mail Addon + Google Apps.

The issue we are having is when sending an email to a lead outside of Zoho, it seems hit and miss to see that email appear in the Lead section in Zoho CRM.

Here is what seems to work:
- when sending email from Zoho CRM Lead page
- when sending email from Zoho Mail page

Here is what seems to work sometimes:
- when sending email from gmail.com

Here is when it does not seem to work (but did when we started):
- sending from a 3rd party email such as Microsoft Outlook

Does anyone else have this problem?