You can easily Save IMAP Server email files using MacUncle IMAP Backup Tool. The tool supports Mac OS Machines.
Start MacUncle IMAP Backup, enter the account credential.
Click here to know the IMAP Host and IMAP Port, and press the log in button.
Select the email folder to convert and choose the respective format from PST, EML, MBOX, HTML, MHT, CSV, OLM, Thunderbird, IMAP, etc.
Click on the browse button in order to store the resultant file in the required location else save the file in default location - Desktop.
Advanced Filter option to backup emails of specific date & Export selective folders.
Then go back to Start IMAP Backup and click on Start Backup.
In a few moments, the live IMAP backup starts and soon the software will notify the conversion completion messages.