[Users] mh folders unexpected behavior

[pq]

I have multiple POP accounts with a MH folder for each one.
When I compose a new email, for any account, always the email is saved
on the SEND subfolder of the MH folder that fall into to first mailbox .
This behavior is unexpected, cuz when I wrote a email on a account X, i
expected that this email saves on the same MH folder. Same problem
with draft email. How to resolve this behavior? 

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pq