Amen Yehei Shmei Raba........

The Mishna Berura 56:16 writes that during Kaddish, we should ideally recite all 28 words until the end, but we rely on the chazzan to be motzi us. my question is, are we actually accustomed to doing this in practice? I haven’t seen people doing it. should I be makpid about saying the whole correct thing myself? Often, I miss hearing the chazzans continuations (because of noise or speed), and even if I try to say the full text, I might end up missing responding Amen because the chazzan goes quickly. Also, in which parts of davening is it considered not permitted to interrupt? Is that only during pesukei dzimra and Krias shema, or are there other sections as well where interruption is prohibited?

Shalom! 

Thank you for your question. 

The Ashkenazi minhag is to respond “Yehei Shemei rabba until….L’alam ul’almei almaya.” as brought in the Mishneh Berureh (Seif Katan 15). Many, especially Chassidim, add the word  “Yitbarach,” as well. Only Sefardim answer until “d’amiran b’alma.” As you correctly note, we are merely to listen closely to the chazzan and not respond the extra words ourselves. 

Regarding your question on interrupting: It is a very broad question. There are different rules for different responses at different points in the davening. But it is almost always allowed to interrupt for “Yehei Shemei rabba….” except during Shemoneh Esrei, between Shema and Baruch Shem, and between Ga'al Yisrael and Shemoneh Esrei.