* Floo Powder: This is a common way to send short messages. A pinch of Floo powder is thrown into the fireplace, and the message is spoken into the flames, which then travel to the intended recipient's fireplace.
* Howler: This is a magical letter that delivers a very loud, scolding message. While not exactly an interoffice memo, it is a form of communication used within the Ministry.
* Magical Pigeons: These birds are trained to carry messages and can travel much faster than regular pigeons.
* The Daily Prophet: While not strictly interoffice, the Ministry does use this newspaper for official announcements and information.
* Patronus Charms: More advanced wizards can send messages via patronus charms, which are essentially animated guardians that can carry short messages.
* The Pensieve: While not for sending messages, the Pensieve can be used to share thoughts, memories, and experiences between Ministry officials.
It's likely that the Ministry uses a combination of these methods depending on the message's urgency, content, and the recipients.
It's also possible that there are other, more specific magical methods of interoffice communication within the Ministry that have not been described in the books.