The most common and most likely answer to this crossword clue is the 10 letter word VALENTINES
I've seen this crossword clue in The Guardian
V
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Buddy explains!
The straight part
We know that "Some February mail/February" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case some february mail/february = valentines.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 VALENTINES mean?
VALENTINES noun- An expression of affection, especially romantic affection, usually in the form of greeting card, gift, or message given the object of one's affection, especially on February 14th.
- A person to whom a valentine is given or from whom it is received, especially on February 14th.