The content is something we've done before:

This time we tried something new and obfuscated our mailbox.

Mess hall

It looks like the boxes were addressed to "Secretary team" instead of "PR department".

What does she mean?

Office building ground floor,

In front of Admiral's office,

these are where the mailboxes were set up.

Umm... Souryuu, did you put anything in there?

Aoba sure is amazing. I'm not sure how I feel about her or those who fell for that.