If you are looking for the best IMAP backup software, I would suggest you try Mailvita IMAP Backup Software. I have personally installed it on my computer and it is compatible with Windows 11, 10, 8.1, 7, and even XP with no issues. This mail backup software for IMAP accounts supports Gmail, AOL, Yahoo, Outlook and Office 365 Mail. When you back up IMAP emails, the mail attachments and mail folders are maintained. Using this backup solution for mail, you can export the mail in multiple formats, including IMAP backup to PST, IMAP backup to EML, PDF, MBOX, MSG, HTML, MHTML, and EMLX. Now, you do not require the internet to open the emails after the backup process, and you can easily access your old mail anytime.