MTAs don't usually have AV built in, it's separate (though in some cases closely integrated, e.g. Exchange + Forefront).
I guess you're really asking which free webmail providers don't scan for viruses. No big provider is going to be that sloppy, and no small provider is likely to still be in business.
So you're probably out of luck with tis approach. Some alternatives:
- You could deploy your own MTA, as per Jeff's answer. This is less work than you'd think, since you aren't doing anything clever, so won't need to do any configuration; out-of-the box postfix will send a mail for you.
- You could fall back on the old messaging admin's trick and type SMTP commands by hand over telnet, but that's a little fiddly when you need to send an attachment.
- You could try using SWAKS.
I think SWAKS will be the best option: they have your exact use case - sending EICAR into an MTA to check the AV is firing - as one of the examples in their documentation!