I have a question for the Rav. Please, if you are able, to answer my question with quotes/facts from Psak Halacha of any Rabbonim where neccessary. Allow me to explain a clear story so you would get the idea. In my community where I live, there are many Tzedaka organizations. Yearly, they send out envelopes with letter appeals asking for charity in honor of Yom Tov. I like to only respond those who offer a freepost service envelope as I can’t afford to pay each stamp for each envelope. I am extremely cautious in giving exact ma’aser amounts from any earnings I get from anyone. So when it is time to give ma’aser, I use these freepost envelopes to send them my ma’aser donation. The question is, since my exact maaser donation will be reduced because they will have to pay for the mail, has my ma’aser payment been fulfilled? Similary, if giving a cheque of a donation from exact ma’aser payment, they would need to pay a bit of each cheque they put into their bank account. Has my ma’aser payment been fulfilled? The final question. Since I learned that one should not give more than your share of what you earn, one can at least give a fifth of their earnings - to those who are wealthy. Since I’m not, I follow the tenth procedure. But then here comes the confusion, people give more than what they should give! When meshulachim comes to my door or to shuls, people openly give coins and vouchers. How do they know if they are giving more than required? Is it against the Halacha and Hashem’s commandment? I hope to hear from you soon Thanks!!
You are doing the proper thing by giving the precise amount of money for Ma'aser, According to the Maran Rabbi Yosef Karo (in Responsa Avkat Rochel 3) that one must be careful not to give less than a tenth and should also not add, as whoever adds subtracts, because Ma'aser has a secret and is a foundation. And it seems that you do not have to be concerned regarding the stamp or the check, because you gave the Ma'aser precisely and the expense of the stamp and check are from their account. Regarding your last question, it should be clear that giving precise Ma'aser does not prevent you from giving more charity. The only thing is that the money you give beyond the amount you give as Ma'aser, should be given as charity not as Ma'aser (Ahavat Chessed Part 2, 19, 3 in note). And not only is it allowed, but it is also appropriate and sometimes even required in emergencies (Ahavat Chessed Ibid 4, & 20, 2. and the Vilna Gaon in his Iggeret). It is good to give a coin to the poor before every prayer as it says: (Psalms 17, 15) "I will see Your face with righteousness" (Shulchan Aruch Yoreh Deah 249, 14). (You can see the entire topic in detail, in Shulchan Aruch Yoreh Deah 249. In Ahavat Chessed of the Chafetz Chaim ibid. And in Sefer Hilchot Tzedaka published on Iyar 5769, in the first part of the book, Kitzur Hilchot Tzedakah 4 and in the source he notes).