Its been a long time since I posted anything here but then, haven't had much to post. However, I recently had a fight with my email management solutions. Thunderbird 32 does not have a Lightning extension available for it. Not good when you rely on your calendar like I do. Also I have discovered that Thunderbird isn't as compatible with Gmail as some other solutions. So I went back to Kmail but did a few things very differently.
As best as I could I made all my email filters at Gmail. Reasons for this is I'm simply tired of making filters. Putting the responsibility on my cloud service (a.k.a. Gmail) means they will always be there regardless of what email client I use.
Thunderbird for some damnable reason did not setup all my gmail folders (Personal and Work were ignored) and that caused me some issues. Kmail, on the other hand does recognize them and loads them.
Nepomuk is the default database for Kmail and as we all know it, and Kmail, are both rather buggy. However, using the IMAP protocol Nepomuk doesn't become a big issue, and Kmail works a whole lot better.
As you can see I have a rather extensive set of folders and sub-folders (Gmail calls them Labels) All folders, filters, and email remain on the Gmail server, Kmail downloads no email (it simply loads the email you are reading like a browser, which is handy.)
Here are the instructions for making labels in Gmail. Here are the instructions for using filters in Gmail.
There is one huge advantage of using Kmail over Thunderbird as well, Kmail actually lets you move email between folders (labels) on the Gmail server. Thunderbird balked on that big time.
If your primary email account is Gmail, you may want to look into this solution.