In the last couple of weeks, I've noticed an increase in the number of spam messages not caught by the gmail spam filter. Before that, I can't remember more than one or two message over the last couple of years making it through - now, it's two or three a day.
Is is possible that I've somehow set something to allow these to not be flagged as spam? Is there a way to reset the filtering to the defaults?
Something to keep in mind is that there is a constant battle between the spam-filters and the spammers. Spam-filters are always upgrading themselves based on stuff behind the scenes as well as what it reported as spam by all their users. Spammers on the other hand are constantly updating their code to get around the constantly updated filters. Like any long-running battle, it ebbs and tides back and forth between the two. For a while the filters will be stronger than most spamming code, then the spammers will figure a way around, and then the filters will update themselves to block the new spamming methods.
It's perfectly normal to see spurts in spam from time to time as this battle goes back and forth with spammers and filters taking turns being better than the other.
What still baffles me is that there are enough people who actually respond to the spam that it is financially worthwhile for the spammers to keep up this battle.
Most likely your e-mail address was caught up by a spammer which isn't taken up in Google's spam list. Just click on the Mark as spam box, so Gmail knows about it. This should stop the spam after a few days.
And remember: Never allow the mails to load images and don't click on any link (and not unsubscribe) nor answer. This shows the spammer that your address is real.
If the spam is not caught because of a filter you set (this is possible) it is shown by a big red box just before the e-mail body starts when you open it. You should then adjust the filter accordingly.
Most probably you've given out your email address on an unsafe forum or have exposed it somewhere spammers can get to it. The filter is automatic on gmail and there aren't settings which let you adjust it.
It's likely that somehow a spam message got 'whitelisted' for you in gmail.
If you report it as spam, the gmail spam filter will fix itself pretty quickly.
I have noticed the same thing, albeit on a smaller scale, and I haven't changed any of my settings recently either.
Under Settings there is a Filter tab where you can Add or Edit/Delete an existing filter. I did not have any filters by default though. The filters you are probably referring to are the internal gmail ones of which must be proprietary.
