Is it mailroom or mail room

A question that has puzzled many a grammar enthusiast!

The answer is: it's a matter of style and convention.

Both "mailroom" and "mail room" are acceptable, but with slightly different connotations.

• "Mailroom" is a single word, often used in American English, particularly in business and corporate contexts. It refers to a room or area where mail and packages are received, sorted, and distributed.
• "Mail Room" (with a space) is more commonly used in British English, and is often used in educational institutions, such as universities or colleges, to refer to a room or department responsible for handling student mail and packages.

In general, if you're writing for a US audience or in a business context, "mailroom" is a safe choice. If you're writing for a UK audience or in an educational context, "mail Room" (with a space) might be more suitable.

Ultimately, both forms are widely understood and accepted, so you can choose the one that fits your style and audience.