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.

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
'der Briefkasten' and 'das Postfach' both have to do with mail, but they are used in different situations. A 'Briefkasten' is on a house or apartment so that letters and newspapers can be delivered. A public 'Briefkasten' is used to send letters. A 'Postfach' is either a rented compartment in a post office or, in the digital context, the place for emails. The words can be confusing because both can receive mail. For regular mail at home, you usually say 'Briefkasten'; for a rented compartment or emails, 'Postfach'.

Die Firma hat ein Postfach bei der Post gemietet.
The company has rented a PO box at the post office.
Nach der Arbeit schaut Lisa in den Briefkasten vor der Haustür.
After work, Lisa checks the mailbox by the front door.