How to differentiate between email and chat documents in lotus notes -

i'm trying extract emails , chat history of person nsf file (lotus notes). i'm using notes.jar. entries in nsf files documents. there way identify document email , document chat. there item named "form" used identify mails (memo), meeting invites (appointment). problem face here both email , chat has form type "memo". kindly suggest me way differentiate between email , chat.

you right: both kind of documents have form memo.
chat- transcripts in addition have item $imtranscript identifies them.

i found out fact, using icon- column of documents- view ($all), chat- transcripts have different icons in view. here relevant part of formula:

@isavailable($imtranscript) & @lowercase(imoriginator) = @lowercase(imowner);  "chattranscriptme.gif"; @isavailable($imtranscript); "chat_transcript_icon.gif";