WindowsWhat is the MBS file format?
.mbs is the mailbox store format used by Opera's integrated M2 email client, which shipped with Opera browser versions 6 through 12 (2001-2012). Each .mbs file represents a single mail folder - such as Inbox, Sent, or Drafts - storing all messages for that account and folder in a proprietary binary container.
The internal format is undocumented and not publicly specified. Opera M2 automatically compresses .mbs files using a gzip-like scheme when the number of deleted messages exceeds an internal threshold, helping to control file growth over time.
Opera removed the integrated mail client starting with Opera 15 (2013), when the browser switched to the Blink rendering engine. Opera Mail was maintained briefly as a separate standalone application until approximately 2016, after which it was discontinued. As of 2026, Opera browser ships no email client, leaving .mbs files as orphaned legacy data with limited migration options.
To migrate messages, Aid4Mail and the MBS2MBX utility (a small Windows tool that converts to standard .mbx format) are the primary options. ABC Amber Opera Converter was a historical alternative but appears to be abandonware as of 2026.
Note: the .mbs extension is also used by Micrografx Picture Publisher for brush shape files - an entirely separate, unrelated format.
Security & safety
RISK: LOWEmail archive format; risk is contained within the email messages themselves (phishing links, malicious attachments stored within). The container format itself is passive.
Format details
in a nutshell- Micrografx Picture Publisher Brush Shape - Brush preset file for Micrografx Picture Publisher, a discontinued Windows bitmap editor acquired by Corel in 2001 and phased out in favour of Corel Photo-Paint.
Programs that open MBS files
Technical details
deep spec| Format type | Proprietary binary email mailbox store |
| Developer | Opera Software ASA |
| Container | Proprietary Opera M2 mailbox (undocumented binary format) |
| Encoding | Binary with embedded MIME message content |
| Compression | Automatic gzip-like compression triggered when deleted-message count exceeds threshold |
| Typical file size | 100 KB - several hundred MB (depends on message count) |
| Folder mapping | Each mail folder (Inbox, Sent, Drafts, etc.) stored as a separate `.mbs` file |
| Associated OS | Windows, Linux, macOS |
| Last active client version | Opera 12.17 (2016, final release with standalone Opera Mail) |
| Conversion tools | Aid4Mail; MBS2MBX (Windows, converts to `.mbx`) |
| Name collision | `.mbs` also used by Micrografx Picture Publisher for brush shape files (unrelated format) |
| Released | 2001 (Opera 6.0 with integrated M2 mail client) |
| Latest version | Opera 12.17 (2016) - last version shipping integrated mail client |
MBS conversions
Community Q&A
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