GNUMail is an open-source, cross-platform email client primarily developed for Mac OS and UNIX like systems. Based on GNUstep, this email client supports POP and IMAP accounts. In addition, GNUMail is integrated with filter options for both incoming and outgoing messages. It has two native file formats, Maildir (messages are organized as subdirectories) and Berkely MBOX (email database file). Talking about security features, GNUMail uses GnuPG email encryption to maintain data security.
Despite being such a great platform, it lacks support for HTML format. Moreover, the presence of advanced platforms like Outlook has also affected its user base. Many organizations, as well as individuals, are now moving their mailbox data from GNUMail to Outlook. However, to achieve such migration, a powerful migrator tool is needed. The most recommended email converter is Kernel for MBOX to PST.
Here are a few instructions that you need to follow while convert MBOX files of GNUMail to PST: