Question: the outlook data file ost has reached maximum size?
Answer: Microsoft has documented the registry keys, entries and values here. There are two registry entries for setting the maximum size that an OST file can grow to: MaxLargeFileSize – to set the Unicode format OST file size limit, up to a maximum of 50GB for Outlook 2010 and later, or 20GB for Outlook 2007 and 2003.