Sending an Email using Organization Wide Address in Salesforce
In Salesforce, click Setup and search in Quick Find for Organization. Click on the option for Organization-Wide Addresses.
Click Add and in the following screen you can designate a Display Name, specify the email address and decide if all or just selected profiles can use the address. Based on the permissions here, it determines if a User can select and use such an address when composing email in a composer in Salesforce. After saving there is a verification step Salesforce requires before the address is available for use.
If a User then navigates to a record, clicks the Send Email, Reply, Reply All or Forward options, and launches the email composer, there is a carat for a drop down menu that will display the organization-wide addresses available to the User launching the composer.