MailStewardLite can help you back up your email messages so that they become available even after they have been deleted from your account. The tool stores copies of your messages including possible attachments in a relational database. This way, you can delete old mail from your account to make it easier to manage and faster to access.
Using the application is quite easy. It scans your mail accounts and retrieves your messages, which then become accessible through a GUI that resembles that of a standard email client. In this respect, it supports importing messages from POP, iCloud and IMAP email accounts that are stored locally by the macOS Mail application. Likewise, it can import MBOX files from various email clients, such as Entourage. Once importing is done, you can scroll the list, sort messages by given criteria or perform a search to find the desired email. Besides looking for a given string in the message body, the tool also supports searches based on date, subject and mailbox. Moreover, you can tag messages and use them as filters later on.
Luckily, there are some aspects you can configure. For instance, it is possible to skip importing messages from the Trash and Junk mailboxes. Similarly, you may decide not to store large attachments. Although MailSteward Lite is configured to skip importing duplicate messages, you can toggle the option off if you want to. more