How Gmail and Outlook users can identify tasks in Salesforce that Yesware created:

You can see the tasks that Yesware logs in the activity history of Contacts or Leads in your Salesforce account. There are different activities that will generate tasks within Salesforce. These different activities can be identified by the Task subjects that Yesware logs.

• Message Sent: [subject of the email] - generated when you send an email with Send to Salesforce turned on.
• Message Opened: [subject of the email] - generated when your recipient opens an email that you originally sent with Send to Salesforce enabled.
• Link Clicked in Message: [subject of the email] - generated when your recipient clicks on a tracked link within an email that you originally sent with Send to Salesforce enabled.
• Attachment Viewed: [subject of the email] - generated when your recipient opens a tracked attachment with Send to Salesforce enabled.
• Reply: [subject of the email] - generated when your recipient replies to an email that you originally sent with Send to Salesforce enabled.
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At the bottom of the "Comments" section of each task in Salesforce, you should see that it says, "Data provided by Yesware," which will confirm that it was synced by Yesware and not some other method.