It depends on the type of direct marketing. Different rules apply to digital direct marketing, telemarketing and advertising mail.
Permission
Sometimes you need your customer's permission for direct marketing, sometimes not. In all cases, direct marketing without your customer's permission is only allowed if the customer is Is an actual customer of yours and it involves advertising your own similar products or services.
So you may not (co-)send advertising from another company. Or for products or services that are very different from what your customer has previously purchased from you.
Digital direct marketing
You may contact your customer via, for example e-mail, sms or app without asking permission first. Unless the person has indicated that they do not want this.
Telemarketing
You may call your customer Call your customer with an advertising offer without asking permission first. Unless the person has indicated they do not want this.
Advertising post
Would you like to send your customer send promotional mail, then you are using your customer's contact information for a different purpose than that for which you originally collected it.
Therefore, you must first assess whether the use of the data is compatible. If yes, you may send advertising mail without first asking for consent. If not, you need consent.
