How to model optional product delivery companies
Assuming tables like:

CREATE TABLE PRODUCTS
( PRODUCT_ID ... NOT NULL PRIMARY KEY
, ...
);

CREATE TABLE DELIVERY_COMPANIES
( COMPANY_ID ... NOT NULL PRIMARY KEY
, ...
, 
);


I assume what you mean by ups;dhl;fedex is a table like:

CREATE TABLE PRODUCT_DELIVERY_COMPANIES
( PRODUCT_ID ... NOT NULL
, COMPANY_ID ... NOT NULL
, ...
,    CONSTRAINT ... FOREIGN KEY (PRODUCT_ID) 
     REFERENCES PRODUCTS (PRODUCT_ID)
,    CONSTRAINT ... FOREIGN KEY (COMPANY_ID) 
     REFERENCES DELIVERY_COMPANIES (COMPANY_ID)
,    CONSTRAINT ... PRIMARY KEY (PRODUCT_ID, COMPANY_ID) 
);


and that seems about right.