Official comment
We have two recommendations. One is to use a naming convention. You may do this already, as most people will try to name their messages with a name significant enough to identify the message. Many of our clients use a prefix on their messages, such as "NC-" for "New Client" messages. We have an article on Naming Conventions that can give you some ideas on setting this up.
The second recommendation is related to the first. You can create Message Groups, just as you create Contact Groups. An easy way is to make a Group based on what is or is not in the name of the message, but you can also create a group based on the Subject, Date Added, Type (ONTRAmail or HTML Email), etc. You can even create groups of messages that were opened at least five times, were created and never sent, etc.
Just as you do with Contact Groups, you have several Conditions you can choose to include messages in the group, such as the Name "Starts With" or "Contains" a certain word.
