Is a person considered sinful if they introduce a man and a woman to each other with the intention of marriage, and then they speak to each other afterwards?

Striving to marry off Muslims is a good deed, and there is no harm in mentioning a specific woman to a man for him to propose to her. There is no sin upon the one who does this if something unlawful according to Sharia occurs between them. However, if it is highly probable that the person is not serious about marriage or transgresses God's limits, then it is not permissible to help him. Rather, help should be extended to those who are highly likely to be serious and desire chastity.