No, εἰ μή cannot be legitimately translated as “such as.” It literally means “if not” and is equivalent to “except.” The word for “such as” (i.e., “for example”) would be οἷον.
9 But I say to you that whoever puts away his wife (except for πορνείᾳ) and marries another woman, he commits adultery, and whoever marries her who is put away commits adultery.
Θʹ λέγω δὲ ὑμῖν ὅτι ὃς ἂν ἀπολύσῃ τὴν γυναῖκα αὐτοῦ εἰ μὴ ἐπὶ πορνείᾳ καὶ γαμήσῃ ἄλλην μοιχᾶται καὶ ὁ ἀπολελυμένην γαμήσας μοιχᾶται TR, 1550
As Sola Gratia mentioned, the Gospel of Matthew is the only gospel to include this so-called exception clause despite an absolute prohibition on divorce occurring in all the other Synoptics.1 Likewise, the apostle Paul states that a woman who were to marry another man while her husband was alive would be an adulteress.2 Hence, divorce after marriage is impossible, for what the omnipotent God has joined no man can sever!3 Only once one party of the marriage has died can the other (living) person marry [again], for the former marriage has been dissolved.4
So, why only Matthew? It is no coincidence that Matthew’s gospel is the only one that features the narrative of Joseph nearly putting away Mary while they were betrothed after he found her to be pregnant.5 The New Testament confirms that betrothal was a distinct stage in the marriage process. The Gospel of Luke refers to Mary as Joseph’s “betrothed wife” (τῇ μεμνηστευμένῃ αὐτῷ γυναικὶ)6 which, if indeed betrothal and marriage were equivalent, such a phrase would be superfluous.
The culmination of betrothal was cohabitation and consummation, when the betrothed couple “came together.”7 But, it was before that consummation occurred—before they came together—that Joseph found Mary with child, and he suspected (as any rational man would) that she was unfaithful during the betrothal process. Mary was at least 3 months pregnant when she returned home from Elizabeth’s.
One would think they could just “call off” the betrothal, just as couples call off engagements today. However, once betrothed, a couple was considered lawfully married, for a contract had already been agreed upon by both parties. The only remaining aspect was the cohabitation and consummation. Therefore, Joseph was required to “put her away” (divorce her) as though they were completely married (so to speak).8
In the Mishneh Torah, Moshe ben Maimon wrote,9
Once the woman is acquired and becomes mekudeshet (sanctified), although she has not consummated her marriage and entered her husband’s home, yet she is married. And the man who comes upon her other than her husband is liable to be executed by the court. And if [her husband] desires to divorce [her], a get is necessary.
וכיון שנקנית האישה ונעשית מקודשת--אף על פי שלא נבעלה ולא נכנסה לבית בעלה, הרי היא אשת איש; והבא עליה חוץ מבעלה, חייב מיתת בית דין, ואם רצה לגרש, צריכה גט.
As far as the exception clause “except for πορνείᾳ” is concerned, πορνείᾳ refers to infidelity before or during the betrothal process. Deu. 22:14 and Matt. 1:18 are related.
I took this woman, and when I came to her, I found her not a virgin.
Now the birth of Jesus Christ was thus: When his mother Mary was betrothed to Joseph, before they came together, she was found having [a baby] in her womb of the Holy Spirit.
In Deu. 22:14, when it was determined that the woman was not a virgin (because no proof was found of her virginity), she is said «ἐκπορνεῦσαι τὸν οἶκον τοῦ πατρὸς αὐτῆς», that is, “to commit fornication in her father’s house.” Notice the verb: ἐκπορνεῦσαι, from the lemma ἐκπορνεύω, which is essentially a synonym of πορνεύω, both of which are related to the noun πορνεία. The woman “committed fornication,” that is, she had sex before or during betrothal. Extra-marital sex is not “fornication” (πορνεία); it is “adultery” (μοιχεία). The singular reason why divorce may occur is due to engaging in sexual intercourse before or during betrothal.
Since no Christians practice betrothal, there is essentially no justification for a Christian to divorce. (To note, Matthew was written to a primarily Jewish audience who did indeed practice betrothal.)
Response to comments:
[Ruminator] Jesus lived at the end of the Torah-centric, temple-centric age. In Matthew 5-7 he is teaching Torah to Jews. His teaching should not be taken as normative for the gentile assembly who is not under the law. For that see Paul.
Jesus promulgated a new law, just as Isaiah prophesied (Isa. 2:3), “...and he will teach us of his ways, and we will walk in his paths, for a law shall go forth the from Zion and the word of Yahveh from Jerusalem.” This new law is his gospel. Isaiah does not speak of the Law (Torah) of Moses, for Isaiah uses the future tense and speaks of a law that shall go forth—from Zion. On the other hand, the Law of Moses had already went forth (in the past) from Sinai. Both Jew and Gentile in Christ are equally under the law of Christ. Finally, both Jesus and Paul declared divorce to be impossible for those who are completely married (i.e., past betrothal and have consummated their marriage). Again, no man can sever what the Almighty God has joined. You can try, but you will fail, and marrying another while your original spouse still lives makes you nothing less than an adulterer, incapable of inheriting the kingdom of God.
1 Mark 10:11–12; Luke 16:18 (also cp. Matt. 5:32)
2 Rom. 7:3
3 Matt. 19:6 cp. Gen. 2:24
4 Rom. 7:2 cp. 1 Cor. 7:39
5 Matt. 1:18–19
6 Luke 2:5
7 Matt. 1:18
8 Jewish Encyclopedia on the entry for “betrothal” states, “The root ארש (“to betroth”), from which the Talmudic abstract ארוסין (“betrothal”) is derived, must be taken in this sense; i.e., to contract an actual though incomplete marriage.
9 Mishneh Torah, Sefer Nashim, Hilkhot Ishut, Chapter 1.3