Shababnikim 101: 3rd Person Greetings

שָׁאנֵי רַבִּי יִרְמְיָה בַּר אַבָּא דְּתַלְמִיד חָבֵר הֲוָה. וְהַיְינוּ דְּקָאָמַר לֵיהּ רַבִּי יִרְמְיָה בַּר אַבָּא לְרַב: מִי בְּדַלְתְּ? אָמַר לֵיהּ: אִין, בְּדֵילְנָא, וְלָא אֲמַר ״מִי בְּדֵיל מָר״?

Berakhot 27b:3

With regard to Rabbi Yirmeya’s conduct, the Gemara explains that Rabbi Yirmeya bar Abba is different, as he was not a mere student of Rav. Rather, he was a disciple-colleague and was, therefore, permitted to act that way. And that is why on one occasion, when Rav prayed the Shabbat prayer early, Rabbi Yirmeya bar Abba asked him: Did you distance yourself from labor and accept the sanctity of Shabbat? Rav said to him: Yes, I distanced myself. And Rabbi Yirmeya did not say to him: Did the Master distance himself, as would have been appropriate had he merely been Rav’s student.

משנה אבות ד׳:י״ב

(יב) רַבִּי אֶלְעָזָר בֶּן שַׁמּוּעַ אוֹמֵר, יְהִי כְבוֹד תַּלְמִידְךָ חָבִיב עָלֶיךָ כְּשֶׁלְּךָ, וּכְבוֹד חֲבֵרְךָ כְּמוֹרָא רַבְּךָ, וּמוֹרָא רַבְּךָ כְּמוֹרָא שָׁמָיִם:

Pirkei Avot 4:12

(12) Rabbi Elazar ben Shammua said: let the honor of your student be as dear to you as your own, and the honor of your colleague as the reverence for your teacher, and the reverence for your teacher as the reverence of heaven.

משנה תורה, הלכות תלמוד תורה ה׳:ה׳

(ה) וְאָסוּר לוֹ לְתַלְמִיד לִקְרוֹת לְרַבּוֹ בִּשְׁמוֹ וַאֲפִלּוּ שֶׁלֹּא בְּפָנָיו. וְהוּא שֶׁיִּהְיֶה הַשֵּׁם פֶּלְאִי שֶׁכָּל הַשּׁוֹמֵעַ יֵדַע שֶׁהוּא פְּלוֹנִי. וְלֹא יַזְכִּיר שְׁמוֹ בְּפָנָיו וַאֲפִלּוּ לִקְרוֹת לַאֲחֵרִים שֶׁשְּׁמָם כְּשֵׁם רַבּוֹ כְּדֶרֶךְ שֶׁעוֹשֶׂה בְּשֵׁם אָבִיו. אֶלָּא יְשַׁנֶּה אֶת שְׁמָם אֲפִלּוּ לְאַחַר מוֹתָם. וְלֹא יִתֵּן שָׁלוֹם לְרַבּוֹ אוֹ יַחֲזִיר לוֹ שָׁלוֹם כְּדֶרֶךְ שֶׁנּוֹתְנִים לְרֵעִים וּמַחֲזִירִים זֶה לָזֶה. אֶלָּא שׁוֹחֶה לְפָנָיו וְאוֹמֵר לוֹ בְּיִרְאָה וְכָבוֹד שָׁלוֹם עָלֶיךָ רַבִּי. וְאִם נָתַן לוֹ רַבּוֹ שָׁלוֹם יַחֲזִיר לוֹ שָׁלוֹם עָלֶיךָ רַבִּי וּמוֹרִי:

Mishneh Torah, Torah Study 5:5

(5) A student is forbidden to call his master by name even out of his presence, provided the name be of note that whosoever hears it will know that it is he; neither should he mention his name in his presence, nor even call others whose name are identical with the name of his master, even as one does with respect to the name of his father; but he should always refer to them with a pseudonym even after their demise. He must not salute his master or return salutation in a manner companions give and return among themselves. The manner to salute a master is to bow before him and say to him in tones of awe and respect: "Peace be unto thee, my master!" If his master saluted him first, he should answer him: "Peace be unto thee, my lord and my teacher.

טורי זהב על שולחן ערוך יורה דעה רמ״ב:י״ד

(יד) אלא א"כ הרב חולק כו'.... עוד מצאתי יש לי להוכיח כשאדם כותב סתם לאדם גדול או מדבר עמו פעם אחר פעם אין צריך לומר לו בכל פעם בל' מר ואם לפעמים מדבר בלשון אתה אין בכך כלום

Turei Zahav on Shulchan Arukh, Yoreh De'ah 242:14

I saw it written that a person should be corrected when they just write the normal name for a great person, though if they are speaking with them or referring to them repeatedly, they don't need to say "mar" again and again; if they sometimes speak in the second person, that's okay.