Determining the actual file name sent when using Send Port Macros

Question

I have a BizTalk 2009 send port that uses the %datetime_bts2000% macro in the file name. When I look at the tracked message event, I don't get the name of the actual file that was sent. I thought I could get it from the context property:

OutboundTransportLocation SFTP://xxx@xxxx.xxx.com:22/Inbound/Encrypted/xxx.xxx.xxx.201101280410324 Promoted http://schemas.microsoft.com/BizTalk/2003/system-properties

It turns out that the date is equivalent to my deployment date... not the actual date time stamp of the sent file.

Where do I find the actual filename generated by the Macro?