4 to 5 minutes is more than likely a bit to big of a file for most email recipients.
youre going to need to reduce the file size to 240x180 or smaller and really crank the compression settings.
generally the best formats for tiny file sizes are either sorenson3 or flv/swf.
you can export both from fcp but to really get the best performance youd be well advised to purchase the sorenson compression suite ($400ish) it does a far better job of both formats AND will produce a stand alone swf file where the free exporter from fcp does not.