The most common and most likely answer to this crossword clue is the 7 letter word MAILBOX
I've seen this crossword clue in Financial Times
M
A
I
L
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More clues leading to the result MAILBOX
Buddy explains!
The straight part
We know that "private letter container" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case private letter container = mailbox.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MAILBOX mean?
MAILBOX noun- A box into which mail is put
- A folder or account for the storage of e-mail; an electronic in-box or mailstore.