Convert an Outlook .msg email into a single MBOX file, keeping all original headers and attachments intact. The resulting output.mbox can be imported straight into Thunderbird, Apple Mail, or compatible command‑line mail tools. The converter processes one .msg per submission; for multiple messages you would need a batch archive tool.

All original headers are retained

The converter copies every Outlook header—standard fields such as From, To, Subject, and Date plus any custom X‑headers—into the MBOX entry. Preserving the full header set means the message shows the same routing information, timestamps, and metadata when opened in Thunderbird, Apple Mail, or any compatible client.

Attachments stay attached and readable

All files embedded in the original .msg, whether documents, images, or other binaries, are encoded into the MBOX record with the proper MIME structure. This lets downstream mail programs detect, extract, and open the attachments exactly as they appeared in the Outlook message, without data loss.

Single‑file MBOX output

Each conversion produces one file named output.mbox that follows the standard mboxrd specification. The file contains the converted message; if the source .msg includes multiple embedded items, they are concatenated inside the same MBOX with the required "From " separator line between logical parts. No extra packaging is needed.

File size scope and temporary storage

The free tier accepts typical Outlook messages up to the published size limit, with larger limits available when signing in with a free Aspose account or upgrading to a paid tier. All uploaded source files and generated MBOX outputs are automatically deleted after a 24‑hour retention period, giving enough time to share the download link while keeping storage short.

Limits and scope

File size scope: Free tier accepts typical Outlook .msg files up to the published size limit; signing in with a free Aspose account raises the per‑file cap
Retention period: Uploaded source files and generated output.mbox are automatically removed 24 hours after conversion

How to convert MSG to MBOX

STEP 1

Upload your file

Click inside the file drop area to upload your files or drag & drop them.

STEP 2

Convert

Click on the "Convert" button. Your files will be uploaded and converted immediately.

STEP 3

Download

Download link of converted MBOX files will be available instantly after conversion.

STEP 4

Feedback

Check conversion results and send us your feedback.

FAQ

Will the output MBOX contain all original Outlook headers?

Yes, the converter copies every Outlook header—including standard fields like From, To, Subject, Date and any custom X‑headers—into the MBOX entry.

Are attachments from the .msg kept intact in the MBOX?

All embedded files are encoded in the MBOX with the proper MIME structure so downstream mail programs can detect, extract, and open them exactly as they appeared in the original Outlook message.

How are multiple embedded messages handled in the single output file?

If the source .msg contains several embedded items, they are concatenated inside the same output.mbox, each separated by the required “From ” separator line defined by the mboxrd specification.

What are the file‑size and batch limits for this converter?

The free tier accepts typical Outlook .msg files up to the published size limit; signing in with a free Aspose account raises the per‑file cap, and paid tiers increase the limit further. Each request still handles exactly one file.

How long are uploaded files and converted outputs kept on the server?

All source files and generated output.mbox files are automatically deleted 24 hours after conversion.

MSG to MBOX

A single MBOX file with full headers and attachments, ready for import into Thunderbird or Apple Mail.