I've been getting those fake Hallmark (and other brands) e-card spams for months, years even.
The only time I ever received a real e-card the email named the sender in the subject line and it was somebody I knew. If the email doesn't say who sent it I delete it as spam without a moment's thought. Most of them get dumped by spamassassin anyway but a few get through.
The spammy ones do contain a virus, or a piece of malware that typically downloads other malware and turns your machine into a slave of somebody's spam-sending network.