What is most likely in the envelope?

an invitation to a special event

a message from a peasant

a note from a former schoolmate

a letter from an admirer

an invitation to a special event

Explanation:

Out of all the options given, the one which is most likely in the envelope is an invitation to a special event.

A special event consists of public events, private events, sporting events, fairs & festivals among others. They are categorized as 'special' events most times because they are outside of the host's normal business activities or programs.

That's doesn't mean they don't still have business objectives, while some special events are purely celebratory, many others are held for business purpose such as marketing, sales, advertising, promotion, e. t. c.

Special events are mostly hospitality or entertainment-based, though not all and are mostly of a social, rather than business, nature, with the exception to few others.