When displaying emails in Thai language in web mail, the characters appear as junk. But once clicking on Reply or Forward, the characters will be displayed properly. This only happens with emails from Outlook (Win/Mac/Web) and these emails are using windows-874 character set. Thai language in the subject always appears correctly though.
If configuring Outlook manually to send emails in UTF-8, the emails will display properly when being displayed by web mail.

We employ a workaround of editing UIxMailPartHTMLViewer.m to make it work.

Step 1:
In file /SOGo/UI/MailPartViewers/UIxMailPartHTMLViewer.m
Insert the following at line number 78
{ @"windows-874", XML_CHAR_ENCODING_ERROR},

After

static xmlCharEncoding
_xmlCharsetForCharset (NSString *charset)

Step 2:
Compile SOGo source code with GNUMake (following SOGo documentation)

Step 3:
Replace binary file name "MailPartViewers" to production server at "/usr/lib/GNUstep/SOGo/MailPartViewers.SOGo/MailPartViewers"
Then restart sogo service