It might be worth switching on the advanced logging for mail as this will show more about what's happening on the mail server when picking up those characters:
If this doesn't help, then it may be something to log with your support provider as it sounds as if we'd need to track down the difference in your particular environment causing this. I wonder if the character set selected for the Oracle database is making the difference in your environment (again found some advice online about this regarding the same exhibited behaviour you describe) so this might be some information to provide along with the regional and language settings for the clients and the mail server.
Sorry that I am not able to offer you a definite answer at this point.
Thanks KarenP, I will log the this issue to our support provider. I'll update the discussion if we find anything.
As an FYI one of our clients, also Oracle has just found the same thing. We are going to try a few bits and pieces to see if we can progress this by changing the environment slightly.
ALTER DATABASE CHARACTER SET to change the charset in the database to WE8MSWIN1252 and all was well. If your current database isn't set to this charset, you may need to export/import.
I think the correct character set for the OOTB database should be part of the Oracle installation instructions [hint]
That is brilliant!
Thank you very much dave, and I'll agree, indicating what character set the database needs to be configure should be included on the installation instructions.