You can check your email with Custom Mailbox just as you do today.
All messages sent to your personalized email addresses will be forwarded to your free Yahoo Mail inbox, so you can continue to receive all of your mail (messages sent to either your free or premium addresses) in one place, using the Web-based Yahoo Mail interface you're used to.
To send a message from your Yahoo Mail inbox using your personalized email address, you can just select that address from the From: menu as you compose your message.
Your New Mailbox
Your email addresses will be associated with a new premium mailbox, which means that if you prefer, you can easily organize your mail by address in different mailboxes. (This might come in handy if you use firstname.lastname@example.org for your business but email@example.com for your personal mail, for example.)
If you prefer to manage your free and personalized messages from separate mailboxes, you can simply stop forwarding messages from your new mailbox. (Note that you'll need to turn off forwarding if you want to manage your email with your own email software.) Learn how to turn off forwarding.
You can easily view your new mailbox anytime from your free inbox. Learn how to switch between mailboxes.
With Custom Mailbox, you can also take advantage of POP support to use your own software (such as Microsoft Outlook) to manage mail associated with your personalized addresses.
If you'd like to begin using POP with your personalized email addresses, you'll need to turn off email forwarding, then configure your email software using the settings associated with your new Custom Mailbox account. Learn how to set up POP.