I found that automated spam filters blocked some things that weren't spam (including on one occasion an invitation to a job interview) and let too many things that were spam through. The automated filter also objected to an e-mail someone sent me that referred to a particular make of buses (named after the city they were built in) in the plural...
You're lucky it's only a dozen - I handle e-mails for a voluntary organisation, and of course our e-mail address is in the public domain. Last time I counted, we average about 25 e-mails a day, about 4 or 5 of which we actually want.
I'm not convinced that blocking senders is effective - many spammers use disposable e-mail addresses, others send e-mails that are faked to look like they are from legitimate addresses (either organisations, or from someone's address book that they have hacked - hence getting what at first glance seems to be an e-mail from someone you know that turns out to be spam - got one earlier this week that purported to be from an acquaintance who died a year or two back)
I use a program called '
pop tray' (it's available as a free download) - means you can preview e-mails in plain text and zap them straight off the server if you don't like them.