MailSteward is described as 'With a single click on the Archive button, MailSteward will archive all of the email in all of your Apple Mail accounts into a database for easy retrieval'. There are more than 10 alternatives to MailSteward for a variety of platforms, including Windows, Online / Web-based, Mac, Linux and iPhone. The best alternative is MailStore. It's not free, so if you're looking for a free alternative, you could try Piler or Mail Backup X. Other great apps like MailSteward are Vaultastic (Paid), EveryCloud (Paid), Dropmyemail (Paid) and KLS Mail Backup (Free Personal).
Cloud Email Archival, E-Discovery & Data Management Solution: Vaultastic is a cloud-based email data management solution to safeguard your email to reduce data risks and improve your compliance posture with advanced ediscovery.
Your one stop mail backup and archiving tool for Mac. Automatically backup mails from Apple Mail, Outlook for Mac, Office 365 for Mac, Thunderbird, Postbox, Gmail, Yahoo and other mail services supporting IMAP and POP service directly on your Mac.
EveryCloud’s cloud based spam filtering service blocks 99.99% of spam, viruses and even newsletters if required. Set spam reports to give users control and view 90 days logs of all inbound and outbound email.
Dropmyemail’s simple user interface allows both techies and non-techies to easily backup their emails. Your emails are fetched using TLS/SSL when available and encrypted and stored securely using 256 bit Advanced Encryption Standards (AES).
KLS Mail Backup is an easy to use backup program that allows you to back up and restore your PROFILE-FILES from Windows Mail, Windows Live Mail, Outlook Express, Mozilla Thunderbird, Internet Explorer, and Mozilla Firefox PROFILE-FILES and more. No Backup of the E-Mails!
SysTools Office 365 Backup utility is meant for saving your Office 365 mailbox to PST. The utility helps you to export your emails, contacts, calendars from Office 365 account to Outlook mailbox to Outlook data file.