Following Benei Yisrael’s successful war against Amalek, who had launched an unprovoked offensive against them, God declared on oath that He would wage an eternal battle against the nation of Amalek (Shemot 17:16). The Mekhilta cites Rabbi Eliezer as interpreting this proclamation to mean that converts from Amalek would not be accepted: “If somebody from any of the world’s nation comes to convert, they should accept him, but [if somebody comes] from the house of Amalek – they should not accept him.”
Many Acharonim raised the question of how to reconcile the Mekhilta’s comment with the Gemara’s account of descendants from Haman working as Torah educators in Bnei-Brak (Sanhedrin 96b, Gittin 57b). Clearly, if Haman had descendants teaching Torah, then either they or an ancestor of theirs had converted and joined the Jewish Nation. How was this allowed, if God specifically proclaimed that no converts would be accepted from Amalek?
Indeed, several writers, including the Chida, in Petach Einayim, contend that this matter is subject to debate, and the Talmud does not follow Rabbi Eliezer’s view. Elsewhere, in his Ein Zokher, the Chida adds that the Mekhilta cites a different interpretation of this verse, in the name of Rabbi Elazar Ha-moda’i, who explained that God here proclaims that He will ensure no descendants of Amalek would remain on Earth. Hence, Rabbi Eliezer’s view is not unanimously accepted even within the Mekhilta, and we may therefore assume that the Gemara does not follow his position.
Others, however, have attempted to reconcile the two sources. Rav Yosef Engel, in his Gilyon Ha-Shas (Gittin 57b), suggests that the Gemara refers to the offspring of a woman from Amalek who had married a member of a different nation. As Halakha follows patrilineal descendant when it comes to the personal status of gentiles, the product of such a union does not, halakhically speaking, belong to the nation of Amalek. Hence, the offspring of this marriage was permitted to convert and join Am Yisrael, but the Gemara nevertheless notes the irony that a biological descendant of Haman became a Torah educator.
Another answer is suggested by the Shevut Yehuda (cited in Torah Sheleima, Shemot 17:16, note 131), who noted that a slightly different version of Rabbi Eliezer’s remark appears in the Midrash Tanchuma (Ki-Teitzei, 11). According to the Midrash Tanchuma, God proclaimed that He would not accept converts from Amalek, as opposed to the version found in the Mekhilta, which indicates that Am Yisrael is not to accept such converts. The Shevut Yehuda explains the Midrash Tanchuma to mean that God, in His contempt for the nation of Amalek, does not instruct us to accept converts from Amalek, as He instructs us to accept sincere converts from other nations. This is not to say, however, that it is forbidden to accept converts from Amalek, and thus it is entirely possible that a descendant of Haman converted to Judaism and was accepted as part of the Jewish Nation.