The email, blunt and to the point, popped into City Hall aides’ inboxes at 12:17 p.m., and the subject line said it all: “2 problems today.”

Mayor Bill de Blasio, it seemed, was not pleased.

In a stern, bullet-pointed missive on Monday, the mayor described a star-crossed attempt at riding the subway to a speaking engagement in Midtown Manhattan. A train never came — and when the mayor resurfaced, his security vehicles were nowhere in sight.

“The detail drove away when we went into the subway rather than waiting to confirm we got on a train,” Mr. de Blasio wrote in the email, addressed to Deputy Inspector Howard Redmond, the head of his Police Department security detail. “We need a better system.”

Mr. de Blasio, who has been making a concerted effort to repair his reputation for tardiness, copied two senior aides on the email, including his chief of staff. The mayor, by accident, added another recipient as well: a reporter for The New York Times.