
das Postfach
mailbox
In a digital context, the personal storage area for incoming emails; the inbox of an email account.
Mein Postfach ist voll mit Spam-Nachrichten.
My mailbox is full of spam messages.
mailbox / PO box
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mailbox
In a digital context, the personal storage area for incoming emails; the inbox of an email account.
Mein Postfach ist voll mit Spam-Nachrichten.
My mailbox is full of spam messages.

PO box
A lockable compartment in a post office that you can rent in order to receive your mail there instead of having it delivered to your home.
Größere Firmen leeren ihr Postfach täglich, um die Geschäftspost abzuholen.
Larger companies empty their PO box every day to pick up their business mail.
The word is a simple compound made up of 'die Post' (post/mail) and 'das Fach' (a small, separate compartment). So it literally means a compartment for mail.
Ich habe ein Postfach bei der Post gemietet, weil ich viel unterwegs bin.
I rented a PO box at the post office because I travel a lot.
To distinguish between the two meanings, pay attention to the context. Words like 'E-Mail' (email), 'digital' (digital), or 'Spam' (spam) point to the digital mailbox. Words like 'Postfiliale' (post office branch), 'mieten' (to rent), or 'abholen' (to pick up) refer to the physical compartment at the post office.
Bitte überprüfe dein digitales Postfach, ich habe dir eine E-Mail geschickt.
Please check your digital mailbox; I sent you an email.
In a digital context, 'Postfach' (mailbox) is often used with verbs such as 'überprüfen' (to check), 'leeren' (to empty), or 'aufräumen' (to clean up). Common nouns in this context are 'Spam' (spam), 'Nachrichten' (messages), and 'E-Mails' (emails).
Du solltest dein Postfach regelmäßig leeren, sonst ist es irgendwann voll.
You should empty your mailbox regularly, otherwise it will eventually be full.
A physical PO box has its own address, consisting of the PO box number and the postal code of the city. This address is used instead of the normal street address for receiving mail.
Bitte senden Sie die Unterlagen an unser Postfach 1234 in Berlin.
Please send the documents to our PO box 1234 in Berlin.
mailbox
In the context of email, Postfach and Mailbox can both refer to the place where incoming messages are stored. Postfach is the more usual term in today's German. Mailbox is also possible in this meaning, but it is less familiar.

Die neue Nachricht liegt im Postfach meines E-Mail-Kontos.
The new message is in my email account's inbox.
Das Programm speichert die neue Nachricht in der Mailbox meines E-Mail-Kontos.
The program saves the new message in my email account's mailbox.