There are several ways to deal with excessive spam.
One is to log in to your email provider directly, usually through a web-based interface. Often there are specific spam filters you can tailor. You can often filter directly based on the sender or the presence of certain words in the subject field or main body of the email. You do not indicate who your email provider is, but most offer something like this.
Also, within Mail, you can set up "rules" to put suspect spam into a designated folder. For instance, I found spam was coming to me from an email address "contact@xxxx.yyyy" where xxxx and yyyy were different for many messages but they were all from a sender starting with "contact@" -- even though the sender indicated is not necessarily the actual sender, I created a rule in Mail to place all such emails from anyone starting with "contact@" in a suspected spam folder. You can also create similar rules to look for words or phrases in the subject or body of each email.