Recently when I’ve tried to forward an email, I’ve been getting a bounced back error: This message has been rejected because it has a potentially executable attachment "xyz" This form of attachment has been used by recent viruses or other malware., or An error occurred while sending mail. The mail server responded: Potentially executable content. If you meant to send this file then please package it up as a zip and try again.
In order to understand what this means you need to realize that:
- When you click Forward the original message is being sent as an attachment.
- The attached original email itself contains an attachment, probably with a
.emlextension. You may not see this atachment, but it’s there.
The .eml extension was originally used by Outlook, but has now become a defacto standard for many email programs. Whenever you send an email using Outlook, the email will contain an .eml attachment. Unfortunately it is possible for an .eml file to contain a virus. So many ISP’s have started to block all mail moving through their SMTP servers which contain .eml attachments.
By default, Thunderbird forwards messages as attachments, rather than as quoted inline in the body of the e-mail. There has been a lot of debate about changing this default.
The solution will depend on the application you use. You have a couple of choices if you use Thunderbird.
Forward the current message inline
Forward the current email as inline by selecting the message, and then selecting the menu Message->Forward As->Inline.
Choose to always forward inline
This will force all forwards to be inline. This setting does not allow you to forward multiple emails as attachments on a single email – use the drag-and-drop method below.
Thunderbird 2.x and newer
Select the menu Options->Composition, and then in the “Forward Messages” select list choose “Inline”.
Old school – Thunderbird 1.x
Use this if you have an older version of Thunderbird, and don’t have the configuration options above.
- Go to the Preferences dialog (Edit > Preferences in Linux, Tools > Preferences in Windows) then the Advanced icon and the General tab.
- Click the “Config Editor” button to bring up the about:config dialog
- Type “mail.forward_message_mode” in the filter
- Change the value from its default value of 0 (send as .eml attachment) to 2 (send in-line with attachments included)
Drag and drop
Compose a message as usual and then drag-and-drop the message to be forwarded from the thread pane into the attachment box. This will rename the attachment to “Attached Message” without “.eml” suffix, which will then pass ISP virus filtering.