Now you have 3 options to archive your mails
1. Manual method- Archive your mails with the help of manual method. But this method has some complications such as your mail files can get corrupted or deleted etc.
2. Online tool- Online tool is not a good option in my opinion because there is a high chance of your data loss and also your mail files can be leaked.
3. Offline tool: I prefer this option because it is a safe, secure and fast way to archive your mails.