Time Machine, MailStore, Duplicati, SyncBack, GoodSync, Postbox, BackBlaze, MozBackup, CrashPlan, MailSteward, imapbox, Mail Archiver X, SysTools Gmail Backup, Duplicacy, Office 365 Export Tool, MigrationWiz, Gmvault, SysTools Office 365 Backup, Horcrux, FSArchiver, KLS Mail Backup, EmailDoctor Office 365 Backup Tool, Vaultastic, Gmailkeeper, FavBackup, Dropmyemail, Stellar Mail Backup, Amic E-Mail Backup, EveryCloud, Backupgoo, MailBase Email Archiving are some alternatives to Mail Backup X.