Pick EML if you want a file that opens almost anywhere, including Thunderbird, Apple Mail and most other email apps. It is also the pick if you are sharing the email, archiving it or moving it off Outlook. Pick MSG if you are staying inside Outlook and want every Outlook detail preserved, such as categories, flags and message class. EML is the open, universal format. MSG is Microsoft’s own format and needs Outlook to open properly. For one email you will reopen in Outlook, MSG is fine. For anything you might open elsewhere, choose EML.
Which Should You Pick
If you just want the answer without the background, here it is. The choice comes down to one question: will this email only ever be opened in Outlook, or might it be opened somewhere else.
What “Save As EML or MSG” Means
You see this prompt when you save or download a single email out of Outlook. On Outlook on the web the button says Download, so the download as EML or MSG meaning is exactly the same choice as Save As. Outlook offers two file types for one saved message, EML and MSG. The dialog does not explain the difference, which is why so many people stop and search for it.
So what does save as EML or MSG mean in practice? Both options save the same email to a file on your computer. The difference is the format that file uses, and that decides which programs can open it later and how much Outlook-specific detail it keeps. Neither choice changes the email itself. It only changes the container.
This is not an Outlook backup and it is not the same as exporting a whole mailbox. Saving as EML or MSG saves one message at a time as a standalone file. For a full mailbox you would use PST or another mailbox format instead.
What an EML File Is
EML is the open, standard format for a single email message. It follows the internet mail standards (RFC 822, later RFC 2822 and RFC 5322), which is why nearly every email program can read it. An EML file holds the message headers, the body and the attachments together in one plain text based file.
Because it is a standard rather than a vendor format, EML opens in Thunderbird, Apple Mail, Windows Mail, eM Client and most other email apps, on Windows, Mac and Linux alike. Those clients store mail in their own MBOX mailboxes, which is the bulk format you move into when leaving Outlook. That portability is the whole reason to choose it. If there is any chance the email will be opened outside Outlook, shared with someone who does not run Outlook or archived for the long term, EML is the safer pick.
What an MSG File Is
MSG is Microsoft’s own format for a saved Outlook item. It stores the same message content as an EML file, plus Outlook-specific properties that the open EML format has no place for, such as categories, flags, the message class and certain Outlook metadata.
The trade-off is compatibility. An MSG file is built for Outlook, so it opens cleanly in Outlook but not reliably elsewhere. Hand an MSG file to someone on a Mac without Outlook or on Thunderbird, and they will struggle to open it properly. Choose MSG when you are working inside Outlook, want to keep full Outlook fidelity and know the file will be reopened in Outlook later.
“The rule we give people is simple. If the email is leaving the Microsoft world, even just to a colleague on a Mac, save it as EML. If it is staying in Outlook and you care about categories and flags, save it as MSG. The mistake we see most often is people saving years of mail as MSG, then switching away from Outlook and finding nothing else opens the files cleanly. EML would have saved them the conversion job.”
Nick Rogers
|
Founder, Univik — building Windows email tools since 2013
Save As EML vs MSG in Outlook, Side by Side
The practical differences come down to compatibility, the metadata each keeps and what opens them.
| Feature | EML | MSG |
|---|---|---|
| Format type | Open standard (RFC 5322) | Microsoft proprietary |
| Best for | Sharing, archiving, cross-platform | Outlook-to-Outlook workflows |
| Opens in | Almost any email client, any OS | Outlook, reliably only Outlook |
| Outlook metadata (categories, flags) | Not preserved | Preserved |
| Attachments | Kept in the file | Kept in the file |
| Typical file size | Usually smaller | Usually larger |
| Needs Outlook to open | No | Yes, in practice |
One honest caveat on both. Neither format saves attachments as separate files. Attachments live embedded inside the EML or MSG, so to get a loose copy of an attachment you still open the email and save the attachment out by hand.
Universal
Outlook only
Why New Outlook Defaults to EML
Here is the part most guides miss, and it is the reason a lot of people are suddenly searching for this. The format you get by default now depends on which Outlook you run.
Classic Outlook for Windows saves MSG. The old File then Save As, and dragging an email to a folder, both produce MSG by default. This is what long-time Outlook users are used to.
New Outlook for Windows defaults to EML. Microsoft’s redesigned Outlook saves single messages as EML, and its drag to File Explorer now creates EML rather than MSG. The old File menu Save As is also hidden behind the More actions menu. This switch surprises people mid-task, which is exactly when they go searching for what EML means.
Outlook for Mac and Outlook on the web save EML. Both save or download single messages as EML. On the web the command is called Download rather than Save As.
So if you recently moved to new Outlook and your saved emails changed from MSG to EML, nothing is broken. The default format changed with the app. In new Outlook you can still choose MSG through the More actions then Save as menu when you specifically need it.
Converting Between EML and MSG
If you already have files in the wrong format, you do not have to re-save each one. You can convert in either direction.
To open an EML file in Outlook and keep it as MSG, you can drag the EML into Outlook, which opens it as a message, then use Save As to store it as MSG. To go the other way, open an MSG in Outlook and save it as EML. For a handful of emails the manual route is fine. For hundreds or thousands, doing it by hand is slow and risks losing formatting or inline images.
For bulk work, a dedicated converter handles the batch in one run while preserving attachments and message structure. Univik builds an EML converter and an MSG converter for exactly this, converting large sets of files between formats on Windows without opening each message by hand.
If you are moving off Outlook entirely rather than converting single messages, the related guides on importing OST into Thunderbird and opening OST in Apple Mail on a Mac cover the mailbox-level move, and the OST converter handles the offline Outlook data file itself.
Have a pile of EML or MSG files in the wrong format? Convert between EML and MSG in bulk on Windows, with attachments and message structure kept intact, without opening each email one at a time.
Frequently Asked Questions
Should I save as EML or MSG?
Save as EML if the email might be opened outside Outlook, shared with someone who does not use Outlook or archived long term, because EML opens in almost any email client. Save as MSG if you are staying in Outlook and want to keep Outlook-specific detail like categories and flags. For cross-platform safety, EML is the better default.
What does “save as EML or MSG” mean in Outlook?
It means choosing the file format for a single email you are saving out of Outlook. EML is the open, universal email format that opens almost anywhere. MSG is Microsoft’s Outlook-specific format. Both save the same message. They differ in compatibility and how much Outlook metadata they keep.
Is EML or MSG better for sharing emails?
EML is better for sharing. It follows an open standard, so the person you send it to can open it in Thunderbird, Apple Mail, Windows Mail or most other clients, on any operating system. An MSG file needs Outlook to open properly, so it can be a dead end for anyone without Outlook.
Why does new Outlook save emails as EML instead of MSG?
The redesigned new Outlook for Windows defaults to EML for single saved messages, and its drag to File Explorer creates EML rather than MSG. Classic Outlook defaulted to MSG. If your saved files changed format after moving to new Outlook, this is why. You can still choose MSG through the More actions then Save as menu.
Can MSG files be opened without Outlook?
Not reliably. MSG is a Microsoft proprietary format built for Outlook, so other email clients do not open it cleanly. To open an MSG without Outlook, convert it to EML first, which opens in nearly any email app. This is a common reason people convert MSG to EML.
Do EML and MSG files keep attachments?
Yes. Both formats keep attachments embedded inside the saved file, so the attachment travels with the email. Neither format saves attachments as separate loose files, though. To get a standalone copy of an attachment, open the email and save the attachment out separately.
Conclusion
When Outlook asks you to save as EML or MSG, the decision is short. Choose EML for anything that might leave Outlook, since it opens almost anywhere. Choose MSG when you are staying in Outlook and want every category, flag and Outlook property preserved.
If you have moved to new Outlook and the default changed to EML, that is expected, not a fault. And if you end up with a stack of files in the format you did not want, converting between EML and MSG in bulk is quicker than re-saving each email by hand.