Who is "email"?
Please notice that the qualifying condition is, "if your brother sins against you". I do not think he "sinned against you". He is a public false teacher, who has subtly advocated multiple errors. This he has all done very publicly! Therefore, it cannot be ultimately resolved privately. Publicly he sinned; therefore, publicly he must at least correct himself or be corrected; otherwise, there is no reasonable effort available to check the error and misleading influence."Moreover if your brother sins against you, go and tell him his fault between you and him alone. If he hears you, you have gained your brother. But if he will not hear, take with you one or two more, that 'by the mouth of two or three witnesses every word may be established.' And if he refuses to hear them, tell it to the church. But if he refuses even to hear the church, let him be to you like a heathen and a tax collector." (Matthew 18:15-17)
Also, please notice the verse that Jesus quoted, 'by the mouth of two or three witnesses every word may be established'. This OT quotation shows up more than once in the NT, but it comes from Deuteronomy 17, which is inserted here for convenience:
As a side note, this passage helps us resolve a related, tangential dilemma: We are not to "police" the brotherhood, but if news comes to us, then judges responsible for such people are obligated to investigate. ... More to the point, in the context, the "witnesses" are witnesses of the sin not the confrontation of sin. In fact, if there are not enough witnesses, the accused gets off for now, even if they are indeed guilty. So, based on the context, any witnesses you took for your second meeting would be superfluous as witnesses, because you have the fact stated in paper, public, observable to all. Now you could take "two or three" as help or even as an arbitrating "judge" of sorts (I Corinthians 6:5), but not so much as witnesses in the context of Deuteronomy 17:6 and Matthew 18:16, unless you want to witnesses to his sinful reaction. ... Lastly, there are some cases that are too hard for us. In those matters, as indicated by this text, we pass them on to God. Since each New Testament Christian is a "priest", then we each have the power to call upon God to see and judge in the cases that we cannot resolve."... and it is told you, and you hear of it, then you shall inquire diligently. And if it is indeed true and certain that such an abomination has been committed in Israel, then you shall bring out to your gates that man or woman who has committed that wicked thing, and shall stone to death that man or woman with stones. Whoever is deserving of death shall be put to death on the testimony of two or three witnesses; he shall not be put to death on the testimony of one witness. The hands of the witnesses shall be the first against him to put him to death, and afterward the hands of all the people. So you shall put away the evil from among you. If a matter arises which is too hard for you to judge, between degrees of guilt for bloodshed, between one judgment or another, or between one punishment or another, matters of controversy within your gates, then you shall arise and go up to the place which the LORD your God chooses. And you shall come to the priests, the Levites, and to the judge there in those days, and inquire of them; they shall pronounce upon you the sentence of judgment." (Deuteronomy 17:4-9)
So, in short, I don't think the pattern of Matthew 18 is relevant here, except maybe only in principle - just as I used Deuteronomy 17:4-9.
Matthew 18:15-17 and Responding to Public Sin
Feel free to post follow-up questions and responses in this thread.