.eml files blocked by mail servers

If an email with an .eml attachment does not arrive and the sender receives a bounce, the server has rejected it on purpose. On cPanel servers, the rejection usually says something like this:

This message has been rejected because it has a potentially executable attachment "mensaje.eml"
This form of attachment has been used by recent viruses or other malware.
If you meant to send this file then please package it up as a zip file and resend it.

If you want to confirm it, look for the message in cPanel > Email > Track Delivery: there you will see the rejection with its full text.

Why it happens

It is almost always a forward. The sender has forwarded the original email as an attachment instead of copying its text into the body of the message. Some programs do this by default, especially older versions of Outlook.

An .eml is a complete email: it can contain HTML, links and other attachments, and some email clients display it without the user opening it. That is why it is widely used in phishing attacks to hide malicious links and attachments and get past filters.

The attachment filter in Exim (cPanel's mail server) rejects .eml by default, along with other extensions with the same risk, such as:

• .exe (executables)
• .bat and .cmd (batch files)
• .vbs (Visual Basic scripts)
• .scr (screensavers)
• .pif (program information)

Solution 1: forward the email normally

Ask the sender to use normal forwarding, which includes the text of the original email in the body of the message. In Outlook:

• Use Forward, not More > Forward as Attachment.
• If Outlook always attaches the original, change it in File > Options > Mail > Replies and forwards. Under When forwarding a message, choose Include original message text.

That way the email arrives without problems and the recipient reads it directly.

Solution 2: compress the .eml into a ZIP

If the original file needs to be sent (for example, to keep its headers), save the .eml on your computer, compress it into a .zip and attach the ZIP. This is what the rejection message itself recommends.

Our servers' filter does not block the ZIP. If the recipient is with another provider, their server may have stricter rules: in that case, share the file with a download link (Drive, OneDrive, Dropbox…).

Create an exception to allow .eml files

If you need to receive uncompressed .eml files, we can create an exception. Bear in mind that:

• It applies to all the email accounts on the hosting plan.
• It affects all senders: it cannot be limited to one account or one specific sender.
• All the accounts on the hosting are exposed to attacks that use this type of file.

If you still need it, open a ticket with support, stating the domain.