Check all the mailboxes and post offices locations in the following link: Post Office Locator. Post boxes (bústies) in Andorra are bright yellow and are usually free standing. In cities, post boxes may have two slots, one for international mail (estranger o internacional) and another one for national mail (resta d'Andorra o nacional).
If you want your mail to be redirected (reexpedir) by the post office, you must visit your closest post office with your name and your old and new addresses. This service redirects national and international mail up to 6 months, depending on your subscription.
In addition to the usual post office services, a limited range of other services are provided including telegrams, fax, online documents (burofax), etc. which allows urgent mailing with recorded delivery.
You can also find telex transmissions and domestic and international giro money orders services.