So, users were getting
Content Encoding Error (content_encoding_error)
Server response could not be decoded using encoding type returned by server.
This is typically caused by a Web Web site hosting presenting a content encoding header of one type, and then encoding the data differently.
For assistance, contact Customer Support.
And they did
Turned out horde comression for some encodings has issues, Solution was editing C:\Inetpub\vhosts\webmail\horde\config\conf.php, and change $conf['compress_pages'] to false (Turn off compression)
Everything works fine for now, If i intend to host any mail on a Windows server that is.