It's possible to send a card for absolutely anything these days: birthdays, anniversaries, graduations, leaving work, starting work, bad day at work, if your hamster died - the list goes on.
But a new line of cards may have landed on an uncovered niche; greetings for cheating spouses to send, and receive.
Mistress Cards has been launched by extramarital dating website Illicit Encounters, for cheating spouses to send to their "secret, special one."
The line of nine cards have retro pin-up girl designs with lines such as "roses are red, violets are blue, forget that I'm married, I'm hitting on you" or "to my mistress" on the front.
The cards can be sent to your other significant other's email address via an online form (so no suspicious email in your sent box) or printed out and posted to them for just £2.50.
Illicit Encounters has stirred up controversy in the past by encouraging "romance" outside of long-term relationships. Its website states that "whether that's the occasional bit of flirtatious chat, a regular coffee date, or a full-blown affair" is up to the users.
The site has been running for ten years and has over 900,000 members in the UK. The cards celebrate all aspects of having an affair, from anniversaries to inviting somebody to start an illicit relationship. The Happy Anniversary card - to celebrate a long-running affair - has a message inside saying "here's to more naughtiness."
Another reads "I want you as my mistress, to brighten up my life, please overlook that I have a wife. My relationship's ending, some would say dead, so let's have some dinner and end up in bed."
Whether the Mistress Cards will catch on and end up available in high street card shops is yet to be seen...