A few points to remember

1. E-mail deliverability is a way to confirm that your company's or user's e-mails reach their target recipient.
2. If you want to keep a record of each e-mail sent to the leads, contacts, opportunities, and other records from a third-party e-mail client, then use Email to Salesforce.
3. Use connected apps to restrict Salesforce1-downloadable apps from accessing specific users.
4. Using a SalesforceA downloadable app, you can check a user's login history.