"Sales Email was Received" is only being logged in a small percentage of lead records for some of our internal users

Sales Email was Recieved will be logged in two cases. 

 

1) When a Sales Insight Outlook plugin user uses the Log to Marketo button.

2) When a email reply is tracked from Sales Connect.

 

Marketo uses the sales activities to store sales activities that are generated from both the Sales Insight and Sales Connect product. 

 

 

Also, even though you use the Send Marketo Email Action,  if you send the email to multiple leads at once, all the acticity history will be logged to the first recipient. 

More details here:
https://community.marketo.com/MarketoResource?id=kA650000000Gue2CAC

 

That will only log for Leads who recieve a Sales Insight email. The email has to be sent by using the send Marketo Email Action in Salesforce or the Outlook Plugin to be able to have that activity. Are the internal users sending a lot of messages in this way? Do these leads have the was sent sales email activity?