With Salesforce for Outlook, you can actually add an email by simply clicking the ADD EMAIL button within Outlook and it will add to the corresponding records by searching the email address as long as the email address is within the person account record. It will be added following the same rules you have set within your Email to Salesforce settings in salesforce, searching the FROM and TO fields.
You can gain greater control over the records your emails are added to by turning on the feature within the Email to Salesforce settings to "Always send them to My Unresolved Items". This way all emails go into a list where you can add to the specific record you intend with confidence.
You can change this setting by:
1) Setup | My Personal Information | Email | My Email to Salesforce
2) Under Email Associations Section, select "Always send them to My Unresolved Items"
3) Click Save
My Unresolved Items can be accessed as below:
1. Right-click the Salesforce for Outlook system tray icon and click Salesforce | My Unresolved Items...
2. Click the popup message that appears at the Salesforce for Outlook system tray icon when items are added to My Unresolved Items.
3. Click unresolved contacts list in the banner on your Contacts home page if you have unresolved contacts.
4. Click unresolved events list in the banner on your Salesforce calendar if you have unresolved events.
5. Click My Unresolved Items in the banner on an individual email that hasn't been assigned to other records.
6. Click My Unresolved Emails in the My Tasks section on the Home tab.
7. Click My Unresolved Items on the My Email to Salesforce page, located at Your Name | Setup | Email | My Email to Salesforce.