The file type (also known as extension) is the part after the last full stop. If you don't tell us what it is, we don't know waht file it is, and we certainly can't tell you how to open them.
.eml is a e-mail sent as an attachment and should open in Outlook Express. But it's suspect that you write that 'some' files have .eml at the and and don't write anything about other endings of other files.
That reminds me of the famous Anna Kournikova virus. It showed as anna_kournikova.jpg, so people thought it was a picture (jpg extension). But, in fact, it was anna_kournikova.jpg.exe (exe extension) and if you opened it, it was a program that put a nasty virus on your hard disk. It's a classical way to put malware on someone else's computer.
The thing to do: go into Control Panel or My Computer or Windows Explorer and find the Folder Options. Then find the view-tab and UNCHECK the option to "hide extensions of known file types". Then the full filenames with extension should show in Outlook Express. If they don't just go to the filemenu to save all attachment to some folder and then go into My Computer or Windows Explorer to see it.
Post back the extensions of the files you can't open, and we'll see if we can help you.
I assume you know that you should NEVER open attachments from a non-trusted source without having them checked by your antivirus. In fact, I would only open an attachment if the message from a known source clearly is a personal message from a known sender referring to the attachment.
Hope this helps.
i am receiving emails from 3 different sources (mainly they are jokes )with attatchments,when i open them it tells me the file is unknwn type and will not open, if i send them on to a friend he is able to open them,can someone help please.some of the files have eml at the end,thx