Birthday card designs stretching back to the 19th century are being published in a new gallery to mark the day when more people are born than any other time of year.
According to the Office for National Statistics, September 26 has been the most popular day to be born over the last two decades in England and Wales.
Royal Mail spokesman David Gold said: "The joy of receiving birthday cards and reading well wishes from our loved ones never gets old, even as we do.
"Birthday cards are still a thriving market in a world that can feel dominated by email and social media.
"We are proud to play an important part in this much loved tradition every single day."
Hand-made and hand-delivered greetings cards became prevalent in 14th century Europe, with some early German examples carved out of wood.
The practice of sending birthday cards seems to have originated in England in the 19th century, with the original purpose of apologising to friends or family for missing a birthday celebration.
The introduction of the postage stamp to the UK in 1840 meant the practice of sending cards became more affordable and commonplace.