If some messages arrive from the Internet looking like scrambled eggs, then you need to save each one as a file, then decode it. This is much less of a problem with current versions of Microsoft Outlook than it was with older versions of Microsoft Outlook and Exchange Messaging.
There are two types of files that may need decoded: uuencoded messages, that for one reason or another did not get decoded by Outlook and winmail.dat files that result from using RTF message format.
The TNEF/winmail.dat decoder tools can be used by non-Outlook users to "crack open" winmail.dat files to recover attachments.
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If other people complain that your messages arrive with gibberish or a mysterious WINMAIL.DAT file, see Outlook is sending winmail.dat attachments to Internet addresses
why does not word doc file send as winmail.dat from my Outlook to aol?
What does it why doesn't it? I'm going to assume you means why your AOL account gets the winmail.dat file... something in the autocomplete record makes outlook think it should always use RTF to that address. Delete the autocomplete entry and select the address from contacts or type it in the To field.
If its a continuing problems, there is a reg key at the bottom of https://www.slipstick.com/problems/outlook-is-sending-winmail-dat-attachments/ that will disable it.