I was utterly confused by this thread until I realized that you must have had a spam filter built-in to your mail client software before.
iPad and most mobile device mail don't do spam filtering on the device. That's a server's job and a properly configured mail server can do it way better (and even respond nearly instantly to new spam addresses via various services out there) than any "heuristic" spam filter running on the recipient's device.
The reason folks are asking for the domain name of your mailbox is they're wondering what crappy mail host isn't already doing this for you in 2011. Or thinking that maybe your mail host has settings to up their sensitivity to spam.
The very best mail hosts give you a way to feed spam messages that do make it through their filters back into their spam filter engine so it can "learn". Usually it's a folder you can copy them to if you're running IMAP or a special address you can forward to if you're using the outdated POP3 retrieval method.
I've been on MobileMe for a while now, but have run my own mail servers in the past and had settled on the services of the folks at Fastmail.fm for a few years before that. They're utterly fanatical about mail services and that's all they did. Mail. Incredibly good.
They were purchased by Opera (yes, the browser folks) a while back and I have no idea if the key people are still there that made that system run like clockwork. I hope so. Well worth the tiny price I paid to host 6GB of mail there for years.
So we're all wondering who this mystery ISP is that's so far behind the times.
Yahoo, Google, all the big names have excellent server-side spam filtering and full-time professionals to take care of all the details of keeping up with the millions of botnet boxes spewing spam by the millions.
Sometimes it's just time for an address change too. Keep the old one open for a while, check it weekly for real messages you care about and migrate everyone else over to the new one. I have one address I've owned the domain on since around 1993 or so that I'll never give up, but when I ran it on my own server, it gets about 1000 spam messages a week. I got good at the filter writing and blocked a lot of country's IP ranges I would never get mail from ever, so about 15 would make it through the filter. The rest were sent straight to /dev/null.
It eventually became a time thing. Do inwant to waste my life fighting spammers or get an hour or two back a week for a few bucks a year. I chose option 2.
