MailStore Home is a free software to archive, restore and migrate your emails.
You can download it on its official website. Since there are many products, here is direct link to this product page.
There are two installation modes:
You can save your emails from a remote server (IMAP, GMail, Windows Live, …), as well as from your mail applications (Outlook, Thunderbird, Windows Mail, …). The last option is simpler since you won’t have to configure the server’s details like host name, password, etc.
Once your account is ready, you can run the backup process. You can also rerun it as much as you like (e.g. once a week, once a month). Here is what the full process is doing:
Every archived email is stored by account (the address). Like that, it is simple to browse in all the mass of information.
The search feature has a lot of parameters. It can check any fields, if there is an attachment and between dates.
In addition to retaining emails for the future, it is possible to automatically delete messages on the server when they are old enough. The archived copy is not affected and remains available locally. This is very useful when resources on the server are limited.
It is good to be able to save the messages, it must also be able to restore them in the event of a disaster. Accounts configured for archiving are not the same ones as for the export. It is therefore possible to copy from one place and send it to another, which is useful to migrate from a web hosting to GMail or Outlook Live.
To send to GMail, you need to use IMAP and here are the instructions to do it.
The only really important point is to check the space you use locally. If your data ever takes too much space, you can delete some messages that you no longer wish on MailStore. Once done, you must ask the software to clean up its database to really free the unused space. This is like emptying the trash.