SQL (mysql)- normalization advice - Best way to design clients / suppliers tables

Hi,
I'm building a new database in PHP / MySQL.

I have often wondered this and wanted to know what others think.

Lets say I'm building a "suppliers" table which holds information about a companies different suppliers.
I'm trying to decide if to build fields such as email address, and telephone numbers into the main suppliers table or whether to create a one to many relationship with a number of subtables.

In most cases suppliers will only have one email address or one main address but there are cases when they will have more.

therefore is it good practise or overkill to build the database table so in fact there are additional tables such as

"postal address"
"email_address"
"telephone_numbers"
all as seperate tables.

then I could even go further and use these tables for other entites such as "customers" etc.

Is this good advice or am I creating unnecessary complexity? is this just going to slow down my database performance and make coding harder as always having to think about linking the tables?

Thanks for any opinion.