What is the IAF file format?
Files with a .iaf filename extension store Internet Account File data - the complete settings for a single email or news account, exported by Outlook Express, Microsoft Outlook (2002-2007), or Windows Live Mail in a proprietary binary format.
.iaf files can contain such data as:
- Email address and display name shown in the "From" field,
- Name and port number of the server for incoming messages (POP3 or IMAP),
- Name and port number of the server for outgoing messages (SMTP),
- Server type, SSL settings and authentication flags,
- User login and obfuscated password.
Although .iaf is a binary file, third-party tools are capable of decoding and extracting data from such files, including passwords. Passwords in .iaf files are only lightly obfuscated rather than properly encrypted, and are not considered to be stored securely; anyone with access to the file can recover the mailbox login.
Account information can be exported to an .iaf file via the "Export account" menu option, transferred to another computer, and imported into a compatible email client. Windows Live Mail and OE Classic both support this workflow. Modern Microsoft Outlook no longer supports the format; Outlook Express itself was discontinued around 2006 and replaced first by Windows Mail (Windows Vista), then by Windows Live Mail. Each .iaf holds the settings of exactly one account - messages, contacts and calendar data are stored separately in .pst or .ost files.
Security & safety
RISK: MEDIUMAn .iaf is not executable, but it is security-sensitive: it contains your mail server login and a password that is only lightly obfuscated, not strongly encrypted. Free utilities can read the plaintext credentials straight out of the file, so treat an .iaf like a saved password - don't email it, store it unprotected, or leave it on shared drives. If you receive an unexpected .iaf, be cautious: it could be an attempt to make you import a malicious account configuration (e.g. pointing your client at an attacker's SMTP server). Delete old .iaf exports once the account is set up.
Format details
in a nutshellPrograms that open IAF files
Windows4 apps
Windows Live Mail
Free Accounts → Import to bring the .iaf account back. (Live Mail itself is discontinued - install only if you still have it; otherwise migrate manually.) 
Microsoft Outlook (2002-2007)
Paid File → Import and Export → Import Internet Mail Account Settings, then pick the .iaf. Only these older versions support .iaf import.
OE Classic
Freemium Modern Outlook Express-style client; its Import Wizard reads .iaf account files - a practical route when modern Outlook won't.
Notepad (inspect only)
Built-in Opening the binary .iaf in Notepad shows mostly gibberish but readable server/username strings - handy to recover server names. Don't expect clean output. Technical details
deep spec| File type | Binary settings export |
| MIME type | application/octet-stream |
| Encoding | Binary, little-endian |
| Developer | Microsoft Corporation |
| Typical file size | 1 KB - 4 KB |
| Accounts per file | One email or news account |
| Password storage | Lightly obfuscated only - not securely encrypted |
| Supported protocols | POP3, IMAP (incoming); SMTP (outgoing); NNTP (news accounts) |
| File signature | No fixed public magic number; identified by file extension and context |
| Platform | Windows only |
| Stored settings | Server addresses, port numbers, SSL flags, authentication type, username, obfuscated password, display name |
| Superseded by | No direct successor; modern clients re-enter credentials manually or use Autodiscover |
| Related formats | .pst (mailbox data), .ost (offline store), .reg (Windows registry export) |
| Supporting applications | Outlook Express, Windows Live Mail, OE Classic, Microsoft Outlook 2002-2007 |
| Released | Late 1990s (Microsoft Outlook Express / Internet Mail and News) |
| Latest version | Legacy format; export removed from modern Outlook (import still possible in Outlook 2002-2007) |
| Specification | fileinfo.com |
IAF conversions
Community Q&A
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