The inboxes get flooded with spam mails and searching for the really useful emails from the junk becomes more and more difficult. Is there some way to stop this other than marking each such mail as spam?
I haven't been bothered by spam for a long time; most services have become pretty good at blocking it.
Are you using a POP3 client or a webmail service?
Besides adding filtering as suggested by "stultuske", you could also try to eliminate its generation in the first place.
Do you have some idea where spammers are getting your address?
Is your email address posted anywhere on the Internet? Do a Google search for your email address and see where it turns up. Then contact the admin of all those pages and ask to have it removed or obfuscated.
There are many ways to reduce spam generated by spambots. Pick one that works for you and use it.
Spam is that stuff which resides in my spam folder and gets deleted automatically without me ever seeing it. Honestly, as far as email spam goes, I cannot recall the last time I saw a piece of genuine spam making it through into my inbox. Just as importantly, I cannot recall the last time I found evidence of any false positives in my spam folder. In fact, so confident am I that genuine mails no longer get flagged as spam that I've pretty much stopped checking that folder now and just let the stuff drop into a big black hole on a rolling basis.
once in a while some new form of spam makes it into the inbox, maybe one every other week or so.
There's false positives though, mostly overzealous spam filters flagging mailing lists as spam because of the volume or masking the original sender.
Overall, the spam volume (including what ends up in the spam folders) has dropped a lot over the last year or two, from hundreds a day to a few dozen a week.
If you get flooded, most likely you signed up for a lot of "newsletters".
I have a spam folder too but I don't have it set to delete without me looking at it. Sometimes good email makes its way there so I'm always watching it. Also, I set up a gmail account and it has (probably) the best spam filter out there. I love it.
When I actually needed to place my email address on a site, I used scr.im. Seemed to work quite well. No more spam than usual.