How to approach potential clients by email?

Hi people… I’m relatively new to freelancing and I was wondering about some tips regarding the approach of potential clients by Email without looking spammy.

I found a bunch of local companies which have some 5 year old plain ugly website and I would like to approach them by email to offer my services to them by proposing them a new and up to date website.
So I’ve send a few email… one by one, not using Bcc or something but none of them ever replied back.

Could some of you experienced freelancers here give me some tips about what to consider and how should I express my self in email so that these companies would take my offer in consideration and not regard my email just like: “Oh no, another Spam got in my Inbox! Delete of course!”

I’m confident that you guys here can help me out with this!

Thanks in advanced,