Sheva Brachos meal:

Ideally, the question of whether a Mechitza is necessary between men and women by a Sheva Brachos meal, is subject to the same debate in the Poskim mentioned regarding a wedding meal[1], by which the Rebbe concluded to be stringent and so is the widespread custom by a wedding meal, and the same should apply to a Sheva Brachos meal.[2] [Nonetheless, for some reason, many are more lenient by a Sheva Brachos meal to not have a formal Mechitza between the men and women. This especially applies if it is not open for acquaintances and friends and is only attended by the immediate families.] Some Poskim^[3] rule that by a Sheva Brachos it suffices to have a Mechitza of ten Tefach between the sides and it is not necessary for it to completely block the sight of the women, and in such a case one may say Shehasimcha Bimiono.

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[1] The original debate was not regarding the wedding meal per se but rather regarding any Sheva Brachos meal and if the blessing of Shehasimcha Bimiono may be recited. Hence, the conclusions brought above regarding the wedding meal should apply likewise regarding any of the Sheva Brachos meal.

[2] See however Hiskashrus 588:11 that perhaps even the Rebbe only referred to a wedding meal, but not to a small Sheva Brachos meal by which one can rely on the Levush ibid

[3] Shevet Halevi 8:281; See Hiskashrus 588:11 that according to the Sefer Chassidim that the intermingling itself is forbidden, perhaps having separate seating suffices and having actual dividers is not necessary. However, according to the Sefer Minhagim Tirana, it is clear that a blocking divider is necessary