MYSQL QUERY OPTIMISATION! QUERY RUN TIME EXCESSIVE

I have a mysql query which loads customers email addresses thru a php script. inside the php script it loads all customer email and usually only takes about 5 seconds then also in the script it loads any emails which have been BLOCKED or BLACKLISTED these come from another table then it allows me to filter the emails and remove the blocked emails from the mailing list before sending emails. BUT HERES THE MAJOR PROBLEM as my blacklist or blocked list grows the query time seems to GROW EXPONENTIALLY ive went from 5 secs with 0 blocked emails to 70 secs with just 300 blocked emails its taking around 5 secs for every additional email i add i had a look at the query it doesnt seem excessive but something is slowing it down i need this looked at to see if we can come up with a way to speed it up. 0 blocked emails page loads in about 5 secs 300 blocked emails page takes over 1 minute to load My MySQL query, which joins multiple tables, is taking too long to run. Unfortunately, I can't share the data it's run against. - The problem: My query takes too long to execute. I need it to run faster without compromising the results. - Query complexity: It involves joins across several tables. An understanding of structuring multi-table queries for optimal performance is needed. - Note: I won't be able to provide a sample data set. However, I can explain the schema in detail. I'm looking for someone with proven experience in MySQL query optimization, a deep understanding of databases management and performance tuning.