He is asking about the ruling on selling the online services he offers
Question

I want to ask you, as there are not many scholars here in the West. I want to ask you: I am a student and a professional in the field of Internet and e-commerce. I want to sell some services to the Arabs in return for five dollars. One of these services is a website that offers the service of selling products through e-mail, meaning a website that offers the service of sending messages to customers and selling products to them, or alerting them to some specific issue. I do not know in which way the purchaser will use it, even though one of the conditions of sale is that he must promise me and swear to me that he will not use this service for any purpose that is not pleasing to Allah. I also sell Facebook pages to him, in which Arabs will communicate with him; I sell that to him, and he is an Arab Muslim, and he promises me and swears that he will never use it for anything that is not pleasing to Allah.
My question is: can I begin to sell the services or not?
Praise be to Allah.Internet services and tools are neutral, meaning that they cannot be described as halal or haram in and of themselves; rather they are judged according to the purpose for which they are used. If someone uses them to do wrong, commit sin and cause harm, then they are haram for him; if someone uses them to do good, benefit people and do permissible things, then they are permissible.
The responsibility of the seller and producer is limited to two small areas:
The first is that during production, he should pay attention to building restrictions into his product so that it cannot be used in haram ways, as much as it is possible to do that. This requires him to be aware of common, widely known haram uses, and the details of the ways in which it may be used, then he has to think of ways to avoid making it easy for people to use it in such ways in his programming.
The second is that you should refuse to sell or offer the service to anyone who you are certain, or think most likely, is going to use it for sinful purposes or to cause harm to others.
But if you do not know what is the case, or you are uncertain about the matter, or you know that he is going to use it for permissible purposes, or you have taken a pledge from him that he will avoid using it for unlawful purposes, then you have absolved yourself of blame, by Allah’s leave.
These details have been discussed previously in many answers on our website, including, for example, questions no. 82593 , 105325 and 169955 .
Shaykh al-Islam Zakariya al-Ansaari (may Allah have mercy on him) said:
If a person sells grapes to someone who will use them to make wine, and he is certain or thinks it most likely that that is the case, and in similar cases where the purchaser will use the item in a sinful manner, such as selling fresh dates to someone who will turn them into nabeedh, or selling aggressive roosters or rams to someone who will use them for fighting, that is haram, because it is something that leads to sin, but the transaction is valid, because the prohibition is not because of the thing sold, but for another reason. But if he is not certain about that, the sale is disliked (makrooh)."(Asna al-Mataalib  2/41).
It remains for us to point out that with regard to selling e-mails and Facebook likes, it is essential to respect people’s privacy and not violate their privacy except in terms of that which is overlooked in the well-known conditions of use in such matters. For more information, please see the following two answers: 135514 and 174411 .
And Allah knows best.