What is the FWD file format?
An .fwd file is a transient spool file created by IMail Server during the message-forwarding process. IMail Server is a Windows-based mail server developed by Ipswitch, Inc., acquired by Progress Software in May 2019 and now marketed as Progress IMail Server.
The file stores the forwarded message as plain text in RFC 2822 format - the same structure used by .eml files - including standard headers such as From, To, Subject, and Received, along with IMail-specific X-IMail-* proprietary headers. Non-ASCII content and attachments are encoded per RFC 2045 (Base64 or quoted-printable MIME encoding).
.fwd files are written to the IMail spool directory as a temporary step and are not intended for end-user access. Administrators typically encounter orphaned .fwd files when forwarding fails mid-delivery or the server is interrupted. Because the underlying format is standard RFC 2822, renaming a .fwd file to .eml allows most mail clients to open it directly.
The file has no fixed binary signature; it begins with standard mail headers and may include X-IMail-* lines that identify it as an IMail artifact. The .msg format serves a similar role in Microsoft Exchange and Outlook environments.
- File size typically ranges from 1 KB to 10 MB depending on MIME-encoded attachment size.
- Non-ASCII characters in headers are encoded per RFC 2047 (encoded-word syntax).
- IMail Server operates exclusively on Windows Server platforms.
Security & safety
RISK: LOWPlain-text RFC 2822 email; the same phishing/malware risks as any email message apply (malicious links, malicious attachments encoded as MIME parts). The file format itself is harmless - no executable code in the container. Treat embedded attachments with standard email hygiene.
Format details
in a nutshell- Generic forwarded email (various mail servers) - Some mail servers use .fwd as a generic extension for forwarded message spool files, not specific to IMail.
- Microsoft Works Spreadsheet - Older versions of Microsoft Works used .fwd for certain document variants - unrelated to email.
Programs that open FWD files
Windows4 apps
NotePad++ text editor
Built-in Right-click → Open with → Notepad to view raw RFC 2822 headers and body text. 
Mozilla Thunderbird
Open-source Rename to .eml, then drag into a Thunderbird folder or use File → Open Saved Message. 
Microsoft Outlook
Paid Rename the .fwd file to .eml, then drag it into Outlook or double-click to open. 
IMail Server (Progress Software)
Paid Native spool file - processed automatically by the server; for manual inspection, open the spool directory and read with a text editor. 
macOS1 app
Technical details
deep spec| Format standard | RFC 2822 (Internet Message Format) |
| Encoding | Plain text, ASCII or UTF-8; attachments MIME-encoded per RFC 2045 (Base64 or quoted-printable) |
| MIME type | message/rfc822 |
| Container | None - raw RFC 2822 plain-text message file |
| Proprietary headers | X-IMail-* headers added by IMail Server to identify forwarding metadata |
| Attachment encoding | Base64 or quoted-printable (MIME RFC 2045) |
| Typical file size | 1 KB - 10 MB (headers + body; attachments base64-encoded inflate size) |
| File purpose | Transient spool file created during IMail forwarding; not intended for end-user access |
| Platform | Windows Server (IMail Server host operating system) |
| Developer history | Ipswitch, Inc. → acquired by Progress Software, May 2019 |
| Compatible rename | Renaming to .eml allows direct import into standard mail clients |
| File signature | None - starts with RFC 2822 headers; no binary magic bytes |
| Released | 1990s (IMail Server early versions) |
| Latest version | IMail Server v12.6 (last known release) |
| Specification | docs.ipswitch.com |
FWD conversions
Community Q&A
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