From MozillaZine Knowledge Base

This article was written for Thunderbird but also applies to Mozilla Suite / SeaMonkey (though some menu sequences may differ).

You can double click on a .EML file in Windows Explorer and have it displayed in Thunderbird if the entry for .EML in Tools -> Folder Options -> File Types is set to use Thunderbird. If you configure Thunderbird to be the default email client it should do that. However, it may also display a "c is not a registered protocol" error message. The "c" in this message is the drive letter, so if you have other partitions you might see other letters.

This bug has not yet been fixed (as of December 2006—see comment #24).

External links

• bug 313457 This bug
• bug 210164 A similar bug when the local mail viewing protocol (maibox://...) sees an instruction to load files that begin with a non-http protocol.
• bug 261559, bug 300393 Bug reports concerning how Thunderbird registers itself as the handler for .EML files.