A grapefruit a day daily mail

A clever play on words!

The phrase "an apple a day keeps the doctor away" is a common English proverb that suggests that eating an apple every day can help maintain good health and avoid doctor's visits. But you've replaced "apple" with "grapefruit" and "keeps the doctor away" with "daily mail"!

I'm assuming you're making a humorous reference to the British newspaper "The Daily Mail", rather than the postal service's daily mail delivery. Am I correct?

Well, I must say, your pun is quite refreshing!