An important detail regarding the invitation to the walimah (wedding feast) via cards.

The Shaykh : We mentioned earlier the condition of specific designation. Is the distribution of cards, which people do today, a form of specific designation? Yes? In any case, sometimes the one who distributes the card does so not to ensure the recipient attends, but merely to inform him, so as not to be rude to him if he is a relative or a friend. This is evident because he does not follow up; for example, he does not say, "Did the card reach you, so-and-so? Then don't leave me out." Therefore, it appears to me that if there is no specific reason necessitating obligation, distributing cards does not constitute the specific designation intended for a person. In that case, the person has a choice. However, if your cousin gives you a card for the marriage of his daughter, for example, then it becomes specific designation for you. This is not because he sent you the card, but because he is your relative. If you were to decline, people would build many things upon that absence. Yes.