Neither rain nor sleet nor passage of nearly a half-century could stop this postal delivery.

A Brooklyn woman was shocked when she received a weathered, kiss-sealed letter last week that her mother sent for her 19th birthday — in 1969!

The wayward letter arrived at the childhood home of Susan Heifetz in Sheepshead Bay on Wednesday, prompting the baffled tenant to seek out the intended recipient.

The man found a phone number online for Heifetz, who works as a real-estate agent, and gave her a call.

"I was like, 'Oh, my gosh,'" Heifetz said, referring to her amazement when she was told about the smooched envelope.

He said, "'I have a letter for you and the only reason I'm trying to find you is because it's postmarked 1969,'" she added.

Heifetz said her late mom commonly sealed letters with a kiss before mailing them, so when she dropped in on the good Samaritan Friday at the East 12th Street building where she grew up, she immediately recognized her mother's lipstick on the back of the envelope.

"I was very emotional about it," she said. "Her Max Factor lipstick 45 years later . . . it hasn't faded."

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