Want to be a better communicator? This one's easy and helps a lot.
If you have two radically differ subjects to cover with one person, send two different emails.
That way, they'll get messages like this:
From: Sebastian / Subject: Scubadiving in Cozumel in June
From: Sebastian / Subject: Required forms for accounting and corporate minutes
That's much better than getting:
From: Matthew / Subject: Scubadiving in Cozumel + Required accounting and corporate minutes
Why? Many reasons. Here's a few:
1. The likelihood that someone is processing both vacation planning and corporate formalities/accounting at the same moment is virtually zero.
2. It's easier to "pick off" one or two of the messages quickly on the go if they're not crammed into the same email.
3. If there's more than one topic, you can get, "Did I get to this other one yet...?" moments.
4. When you get a reply, you know what topic it's about.
5. Easier to skim to see what needs to be done still.
6. Easier to search and find the relevant messages later.
I recommend you do this even if you have four or five unrelated subjects.
You can of course group messages together if they're very similar ("Agendas for the next two weeks," similar kinds of paperwork, reports/resources on the same topic) or if no action is required.
If there's no action required and it's a "just giving you a quick update" message, I like to start the message with "No action required, just keeping you in the loop" so the person can archive it after reading without thinking.
Break up your messages! It makes people's lives much easier. It only takes a few seconds more, and it's much better than having one gigantic message with a million things going on. It's often little communications upgrades that make you a better communicator, so jump on this one and stop sending people "War and Peace" length messages covering eight topics!