Less is more, but sometimes you have to provide depth. Instructions, clarifying... maybe they just want it in writing. Sometimes, we have to stretch our length tolerance.
Bottom Line on Top
I don't care if they're looking for several answers. Give them the bottom line at the top. Give them the TL; DR.
What's the TL;DR?
TL;DR means too long; didn't read.
Recognize that they'll likely open the message on their phone. They'll catch the first paragraph and save the rest for later.
Ensure they get the most important things they need to know at the top. A good rule for what goes into this pseudo-summary?
Any requests
Highlight where you need clarification
Deadlines
Set the expectation of what's in the note
Address concerns, but save a deeper explanation for later in the note.
Our advice with Longer emails?
1. Pick up the phone.
Regardless of whether you need to send a longer email or not. Following or preceding it with a call is a great way to show you care and manage expectations.
2. Use bullet points
They're extremely effective for visuals. No one wants to read a giant block of text. If you break your points into clean bullets, it's easier for people to follow.
3. Keep it clear
Don't allow the length to let you fall into the trap of using complex sentence structures and words. You can write a book at a 5th-grade reading level. Keep your writing style from slipping.
Comb through your "long email" a few times before you hit send. After a few editing rounds, you'll be surprised how often that "long email" falls under 250 words.