MimeMessage decodeTextPlainPart() error

[function2000]

when use decodeTextPlainPart(), sometime it return below error:

[ERROR:flutter/runtime/dart_vm_initializer.cc(40)] Unhandled Exception: FormatException: Invalid character (at character 5) This is a multi-part message in MIME format.------=_NextPart_4CA2B3AA_08661...

I searched via AI, it says, this could be multipart reason. Can you please check and fix this issue? Thanks!