harmon.ie allows you to easily upload incoming and outgoing email messages to SharePoint, using drag and drop, or with the Save Message and Save on Send ribbon buttons.
A few configurations in harmon.ie and in SharePoint allow you to better capture and classify emails uploaded to SharePoint:
You can disable the harmon.ie option Ask me to save email when I send it then the user will always be prompted to save an outgoing message to SharePoint.
To do that, set PromptToSaveEmailOnSend provisioning key to Always, and add the Force = 1 value.
If a message was previously saved to SharePoint, harmon.ie tries to automatically save the replied or forwarded message to the same SharePoint location. You could configure harmon.ie to automatically save email attachments next to the email message, and replace them in the email message with links.
To enable these features set the SaveConversationInTheSameLocation and/or PromptToReplaceAttachmentsWithLinks keys, as explained in Provisioning email upload options.