[horde] MIME and plain text message

[Dmitriy MiksIr]

Hello.
How i understand, all IMAP messages parsed by MIME library. When the 
create MIME Part, charset from this MIME part of message used.
But if message plain/text - which charset will be used - default or from 
headers of message?
This question because i got troubles with display plain text 8bit 
letter. How i understand, used default charset (us-ascii) even if 
charset= set in content-type of message, isn't it?