Happy Monday of postcards

thanks.

A. Same as for Rosh Hashanah, two days?
B. To what extent is this a practical halakhic practice (not from the perspective of the halakhic perception of Judaism today)? That is, would we say this is at the level of a small thing that can be revoked personally? (Clearly, these are two completely different things and the reason for the permit is also different)

A. There is no difference.
B. No. This is a rule that was established in the Great Court and a person cannot revoke it even if the reason is invalid. This is not a rule, but rather a concern that was practiced at some time and was not determined by an authorized court. See my article on legume.

It is not clear that this is a rule established in the Great Torah; simply put, it is a normal rule of doubt from Torah to the grave, which was practiced when there was truly doubt (that they sanctified based on the evidence).
Even if it were said that this was a regulation in the Great Testament, the basic premise of the Gemara was that while there is no doubt, it is possible to cancel the second Yot, but rather, "Send them from the grave, be careful in the custom of your ancestors, lest the matter return to its corruption." According to my historical calculation, the "Send them from the grave" is not in the Great Testament (if it were in the Great Testament, they would sanctify them based on evidence, and there would be genuine doubt).
Rashi explained that lest the matter return to its corruption – that the secret of the conception would be forgotten (and they would return to the holy according to the evidence).
Nowadays, even if things were to go back to their former glory, the Diaspora would know very quickly when the month was sanctified, and there would be no need for emissaries to travel for several weeks to announce when the month was sanctified.
Therefore, there is no point today for Yot Shani (since there is no fear that the matter will return to its desecration), and there is a point for two good days of Rosh Hashanah, for exactly the same reason as the Gemara – lest the matter return to its desecration, and they will not be able to send a WhatsApp on Rosh Hashanah to announce that the month has been sanctified.

The Gemara makes it clear that this is a rule and not just a satisfactory practice. Regarding Reh, there is a Rishonim method that does not require two days.

A. Where is such a gemara? After all, this is the subject of the assumption that the eruvi tevshilin and the eruvi tekhumin are sufficient, which discuss the desolation of your soul, one of which is a sand.
B. Even if you find such a Gemara, I have already addressed this and written that the Gemara explains that in practice Yot Sheni would have been abrogated if it had not been for "Be careful in the custom of your ancestors," and this statement was certainly not stated in the Great Bible.
C. Regarding Rosh Hashanah, there are indeed some leaders in the Land of Israel who make light of it, and I have not understood their reasons; abroad, there is no one who makes light of it.
And the sermon to Dina that there is a point to Rosh Hashanah at this time, at least abroad, and not to the rest of the second New Year.

Regarding the R.H., we discussed that it is one sanctity, and it is proven by the Hadith that it is a regulation. And regarding the remaining 19 things are explained in the Bitzah issues (this is how the whole issue goes. There too, they disagreed whether it is one sanctity or two, and this is not just a discussion of the laws of spikot). When I talk about a regulation, it is not necessarily in the Sanhedrin but in the Talmud, which has a law like the Great Council. Be careful, the custom of your ancestors is at most a reason for the regulation (like the Temple being built soon, which is also a reason for the regulation, and therefore even if it is invalid, it does not mean that the regulation can be canceled).
And see the explicit statements in the Rambam, "Kiddush of the Month," 5:55, and "Yot" 1:121.
Although I wrote in the trilogy that there is room to repeal regulations that, due to the repeal of the reason, have become law and do not belong at all.
And regarding a message in the Lord's Supper, there is no problem sending a WhatsApp message on Shabbat if they have completed the Shabbat and sent messengers on Shabbat. Therefore, there is no point in these regulations at all nowadays, and the situation will not return to normal.

In the Book of Tanya (Igeret Hakodesh, 26), it is explained that the second Yom Tov is not merely a reminder of the lack of time during the Kiddush of the month, but rather carries a special divine light that is not revealed on the first day:
"And here is a second Yom Tov of greetings, which has an advantage over the first Yom Tov, being an addition of light from a higher level" – that is, it is an additional divine revelation and not just a technical regulation.
Similarly, in Lakutei Torah (P. Amor, 2:11) it explains that Yom Tov Shoni is connected to a special spiritual enlightenment that came as a result of the stay in exile:
"A second good day of postcards is a light that lingers from the first day and sparkles on the second day" – which clarifies the necessity of the day even when there is seemingly no technical need for it.

Not only is Yom Tov Sheni relevant, but it also expresses a deeper connection to holiness, especially in a generation of concealment. In Hasidic books, it is explained that the exile itself created tools for receiving a higher light during these days, and therefore its cancellation based solely on "rational" reasoning reveals a lack of understanding of the spiritual nature of the custom.
Ignoring the Kabbalistic foundations of Yom Tov Shani and making it "irrelevant" reflects a superficial approach to Jewish heritage. Beyond simple halacha, this day serves as a tool for discovering a higher divine light, as explained in the teachings of Kabbalah and Hasidism. Only someone blind to the spiritual level of the mitzvot could claim that it is unnecessary.

Obviously. In the book Likuti Amrei, I expanded on this by saying that the second Yot is also meant to prevent obesity, beautify the body, and increase wealth, as well as to establish peace among the swans in the sick lake. Only someone who is blind to these theses could think that it is only meant to add divine light.