Why have I started receiving in excess of 200 spam message per day?

I have always received  some spam message in my Junk folder and accepted that.  However, within recent months I have been receiving well over 200 spam per day.  My concern is that some legitimate emails are also being sent to the Junk folder instead of my Inbox.   I try to block as much spam as possible but it has become tiring since the spam senders modify their domain name by 1 character/digit so a huge amount of  spam gets through.  I would like to set my preferences to delete ALL spam but unfortunately some legitimate emails arrive in the Junk even though they are listed in my Contacts and also  as 'safe' in my preferences under 'safe and blocked' senders.  I don't want to lose legitimate emails hence opted not to set my preferences to delete all spam immediately.  I don't want all this spam and would appreciate it you can advise how can this be resolved.

Thank you.