class MailableEvent < ApplicationRecord
   has_and_belongs_to_many :email_addresses
end

class EmailAddress < ApplicationRecord
   has_and_belongs_to_many :mailable_events
   validates :address, uniqueness: true
end

...
email_address_array.each do |address|
   @email_address_obj = EmailAddress.find_by_address(address)
    unless @email_address_obj
       @mailable_event.email_addresses.new(address: address,unsubscribe: false)
       @mailable_event.save
    else
       @mailable_event.save
       event_fk = @mailable_event.id
       email_fk = @email_address_obj.id
       sql_insert = "INSERT INTO email_addresses_mailable_events("mailable_event_id", "email_address_id") VALUES(#{event_fk},#{email_fk});"
       ActiveRecord::Base.connection.execute(sql_insert)
end

> Look up first email address in email_addresses table and load it in.  # @email_address_obj = EmailAddress.find_by(address: 'something@gmail.com')

> Save the record({ serial number '456'}) associating it with 'something@gmail.com' too # @email_address_obj.mailable_events.create(@mailable_event.attributes)

> Look up second email address in EA table and load it in.  # @email_address_obj = EmailAddress.find_by(address: 'anything@gmail.com')

> Just associate the record({ serial number '321'}) with 'anything@gmail.com' # which means nothing has to be updated in Models and only a new entry { id: 'xx', EE_FK: 'xx', EA_FK: 'xx' } in join table has to be inserted, for which I cannot use @ea_object.mailable_events.create(@mailable_event.attributes) coz it will create a new duplicate EE record.