Convert EML to MSG — Outlook files written in your browser
The EML to MSG converter turns standard .eml emails into Outlook .msg files. It writes a real Outlook compound file — the structure Outlook uses when you save a message — with the subject, sender, recipients, dates, plain-text and HTML bodies, attachments, inline pictures and the original Internet headers.
People need this when a company archive, an e-discovery portal or a colleague insists on .msg, when moving messages from Thunderbird, Apple Mail or Gmail into Outlook folders, or when a document-management system only indexes Outlook items.
Every file is checked before you download it: it is read back and compared with the original email, and the result is shown on screen. Nothing is uploaded.
How to convert EML to MSG
- Drop .eml files — or an .mbox mailbox to convert every message in it — on the upload area, or press Try a sample email.
- Preview a message to make sure it is the right one.
- Choose whether to include attachments, keep the Internet headers and store X- headers as named properties.
- Press Download .msg. Several messages arrive together in a ZIP.
- Read the Read-back check and open the table of every MAPI property that was written.
EML to MSG features
A genuine Outlook file
A compound file (MS-CFB) built with the cfb library (Apache-2.0), holding the property streams and storages described in Microsoft’s MS-OXMSG specification.
Unicode throughout
Subjects, names and bodies are stored as Unicode strings and the HTML body as UTF-8, so Hindi, Chinese and accented text survive.
Attachments and inline pictures
Each attachment is stored by value with its name, type and size; pictures used in the HTML keep their Content-ID and are hidden from the attachment list, as Outlook does.
Headers preserved
The original header block goes into PidTagTransportMessageHeaders, and X- headers become named properties in the PS_INTERNET_HEADERS set.
Verified before download
Subject, sender, recipients, bodies, date and attachments are read back from the finished file and must match exactly, byte for byte.
What is written into the .msg
| Part | MAPI properties (MS-OXPROPS names) |
|---|---|
| Message | PidTagMessageClass (IPM.Note), PidTagSubject, PidTagSubjectPrefix, PidTagNormalizedSubject, PidTagConversationTopic, PidTagImportance, PidTagMessageFlags (read), PidTagHasAttachments, PidTagStoreSupportMask (Unicode) |
| Sender | PidTagSenderName, PidTagSenderEmailAddress, PidTagSenderAddressType (SMTP), PidTagSenderSmtpAddress and the matching PidTagSentRepresenting… properties |
| Recipients | A storage per person with PidTagRecipientType (To, Cc, Bcc), PidTagDisplayName, PidTagEmailAddress and PidTagSmtpAddress; plus PidTagDisplayTo, PidTagDisplayCc and PidTagDisplayBcc |
| Body | PidTagBody, PidTagHtml (UTF-8), PidTagInternetCodepage 65001, PidTagNativeBody |
| Dates and IDs | PidTagClientSubmitTime, PidTagMessageDeliveryTime, PidTagCreationTime, PidTagInternetMessageId, PidTagInReplyToId, PidTagInternetReferences, PidTagTransportMessageHeaders |
| Attachments | A storage each with PidTagAttachDataBinary, PidTagAttachLongFilename, PidTagAttachExtension, PidTagAttachMimeTag, PidTagAttachContentId, PidTagAttachmentHidden, PidTagAttachSize and PidTagAttachMethod |
| Named properties | The __nameid_version1.0 storage with its GUID, entry, string and hash streams |
Outlook compatibility: what is and isn’t verified
The cfb library re-reads the finished compound file, and msgreader — an open-source Outlook reader (Apache-2.0) with its own file parser — reads every property back for comparison. The layout follows MS-OXMSG, and the root storage carries Outlook’s message class ID.
A web page can’t run Microsoft Outlook, so opening these files in Outlook itself has not been tested here. Things to know before converting a large archive:
- No RTF body is written. Outlook 2007 and later display the HTML body; very old versions that rely on RTF may show the plain-text body instead.
- Sender and recipients are plain SMTP addresses without Exchange entry IDs, so they are not linked to your address book.
- An email attached to an email is stored as an .eml file attachment, not as an embedded Outlook item.
- Signed or encrypted (S/MIME) emails are converted as they are: the signature file stays an attachment and is not valid in Outlook.
Related conversions
- Read Outlook files on any device with MSG to PDF.
- Make a readable archive with EML to PDF, or plain text with Email to TXT.
EML to MSG FAQ
How do I convert EML to MSG for free?
Drop your .eml files on this page and press Download .msg. Each email becomes one Outlook .msg file; several are delivered as a ZIP. There is no sign-up or watermark.
Will the .msg files open in Microsoft Outlook?
They follow Microsoft’s MS-OXMSG format and pass a read-back check with two readers, but we could not test them in Outlook itself. Outlook 2007 and newer should show the HTML body — try one file before converting a large archive.
Are attachments and inline images kept?
Yes. Attachments keep their original bytes, names and types, and pictures in the HTML keep their Content-ID so the message can show them in place. Untick “Include attachments” for smaller files.
Can I convert a whole mailbox to MSG?
Yes. Drop an .mbox file and every message in it becomes its own .msg, downloaded together as a ZIP.
Do I need Outlook or Windows?
No. The converter runs in any modern browser on Windows, Mac, Linux, Android or iPhone.
Is my email uploaded?
No. The .msg files are written entirely in your browser. Only the open-source libraries are downloaded from a CDN.