Multiple Sent Folders

I use an iOS Device, MacOS Mail, Outlook, and Thunderbird, and as a 
result, I have three different mail folders:

Sent
Sent Messages
Sent Items

No matter how many times I consolidate them and change my client 
settings to not do this again, I invariably end up with a repeat of this 
problem at some point in the future, be it due to a device change, 
update, or who knows what.

Does anyone have a recommended method to deal with this?

Many thanks,

Tom

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