Check out this page: http://firechewy.com/blog/archive/2005/10/13/924.aspx
I would imagine that one of the following will help you by including the macro in your send port configuration.
| %datetime% | Coordinated Universal Time (UTC) date time in the format YYYY-MM-DDThhmmss (for example, 1997-07-12T103508). |
| %datetime_bts2000% | UTC date time in the format YYYYMMDDhhmmsss, where sss means seconds and milliseconds (for example, 199707121035234 means 1997/07/12, 10:35:23 and 400 milliseconds). |
| %datetime.tz% | Local date time plus time zone from GMT in the format YYYY-MM-DDThhmmssTZD, (for example, 1997-07-12T103508+800). |