Emails sent by OUTLOOK cannot be opened in attachment emails received by other email software and do not have the eml extension

Question

Emails sent by OUTLOOK cannot be opened in attachment emails received by other email software and do not have the eml extension After downloading and saving attachments to the desktop, the file type should be: file, not eml

Answer 1

Dear @Clark Sienna,

Based on your description, this sounds like Classic Outlook is sending/attaching emails as Outlook message files (.msg) instead of the standard.eml format. Many non-Outlook mail clients cannot open .msg files correctly, so when the recipient downloads the attachment, it may appear simply as "File" or an unknown attachment type rather than an .eml file.

To help narrow down the issue, could you please provide the following information?

1. What email application is being used on the recipient side when the attached email cannot be opened? (For example: Outlook, Gmail, Thunderbird, Apple Mail, etc.)
2. Does the issue occur with all attached email files, or only with specific emails?
3. Is the issue reproducible when sending the same attached email to multiple recipients using different email platforms?

In the meantime, to help isolate the issue, please check the following:

1/Verify the attachment format

Save the attached email to the desktop > enable File name extensions in Windows File Explorer.

Confirm whether the file extension is:

• .msg
• .eml
• .dat (Winmail.dat)
• No extension at all

2/Check the message format in Outlook

Go to File > Options > Mail.

Under Compose messages, verify the format being used:

• HTML (recommended)
• Plain Text
• Rich Text Format (RTF)

If RTF is being used, try switching to HTML and test again, as RTF can sometimes generate Outlook-specific attachment behavior.

3/Test by saving and reattaching the email

• Open the original email.
• Select File > Save As.
• Check whether Outlook saves the message as Outlook Message Format (*.msg).
• Attach the saved file to a new email and test delivery to the affected recipient.

Looking forward to your update

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