Indeed, Iam not etirely sure if this rule applies in a professional context. @user111388. Putting the highest ranking person first seems reasonable as you and the answer state.

Hi Ubuntix, I edited your title, because "assistant" in the sense you used it isn't clear. (As you wrote it, "his assistant" meant something like the person who does his scheduling and paperwork). Please feel free to change it if you think I didn't capture your meaning. Same thing with "research assistant" - this is usually a student or person with a bachelor's degree. I assume your second supervisor has a PhD because of your examplees.

Are your fellow students and other colleagues also addressing their supervisors as “Prof. Dr.”? This is very unusual given the circumstances you’ve described, and I’m wondering whether it’s really expected of you. I’m not suggesting you just drop this form of address but I suggest you try to find out what the expected etiquette at your institute is (ask colleagues at the same level!), because it likely isn’t this. Even world-famous researchers are usually addressed by first name and informally in a research context by their colleagues (in STEM, in Germany; more so when speaking English).

Hi @AzorAhai--hehim yes everything you have assumed is correct. Thank you very much for your corrections.

@KonradRudolph I tend to overthink situations like the ones described in my question. Asking some of my other colleagues seems to be a good suggestion. I have not stated that in my question, as I was more concerned with the order of greetings (man or woman first in this case), that my supervisors do not adress me with my first name either. So I think as long as they do not start doing that, our relationship remains at a formal stage. However, I am not quite sure if using their full titles is really necessary. I just want to show respect for their scientific achivements.

I would simply write "Dear all". It's informal but not familiar, and avoids all possible faux pas regarding how individual people are addressed. (Disclaimer: although I've worked in Germany I am English, and don't feel I understand German culture well enough to post this as an answer rather than a comment. But, especially if you yourself are not German, it's hard to imagine anyone being seriously offended by it.)

@TheoreticalMinimum It is neither weird nor old fashioned to greet women first.

@user91988 Are you saying it's usual to greet women first? What culture are you in? Because in mine, greeting women first has no connotations whatsoever (I would never notice)

@AzorAhai--hehim You live in the US, so yes, it does. You may never notice, but the cultural thing to do is list women first in a list of otherwise equals. I didn't make the rules; that's just what people do.

@user91988 No, I have never heard that, I've never seen anyone do it, and would not find it weird if someone greeted a man before a woman in a set of equals. I am young though, so probably it is more old-fashioned than you think.

@AzorAhai--hehim I'm only 30. Here's an example: you are telling your boss your plans. In polite speech, you might say "Stacy, Matt, and I are going out for happy hour after work." Listing Matt first would be considered less polite or "less correct". This has not changed in the last 30 years, believe me. I don't personally care, but someone who feels like they really know English well might. As always, you should keep your audience in mind when speaking. I also very much doubt you've never seen anyone do this. You probably just don't realize because it's so common.

@user91988 Haha, I don't need an example, I understand the basic concept of addressing a woman before a man. (In any case, that's not greeting anyone, that's listing people.) Again - I think greeting a woman first isn't weird (as in no one I can think of would notice), but insisting on it is certainly old fashioned.

@AzorAhai--hehim Well, same thing. Greeting people is just a list of people's names after a greeting. I don't insist on it, but if you want to know what's considered "correct" in English (as much as anything can be considered correct in English), that's it.

@user91988 Well, no. But are you claiming the same rule applies? In any case, I won't dissemble any longer in the comments, but it is not necessary to teach an L2 speaker of English to greet women first in the USA.

@AzorAhai--hehim Yes, the rule applies for any list of people, including a greeting, which again, is just a list of people. I agree it's not necessary to teach. I don't even agree with the rule. But that is the rule, and it hasn't changed in the past 30 years despite your personal opinion.

@user91988 If I wasn't taught it, and none of my peers recognize it, then I consider that having changed.

@user91988 citation needed. You claim this holds, several people myself never heard of this. Sorry, but you are not authoritative source by yourself

@user91988 Native English speaker in America-- if someone tried to tell me that I was "wrong" because I recited a group of names in some random arbitrary order instead of sorted by gender, I think I'd probably laugh until I realized they were serious, and then look at them like they were insane. Possibly this is some specific regional peculiarity, or a habit that was passed down to you by your parents?

@Onyz: I know this rule (about German) too. I googled and I found this site: sekretaria.de/bueroorganisation/korrespondenz/din-5008/anred‌​e which says "in private letters woman first, in business letters the"highest" person first" (I am not sure if you doubting the German or English thing)

@Onyz I'm not saying it's "wrong", I'm saying it's not standard. There is no "wrong" when talking about English.

I never heard about anything related to name ordering (rank or gender) in English other than when it comes to publishing papers (where the author with the largest part in the project goes first sometimes), maybe it's something that only gets taught in high level English courses in college. I've been just referring to names in nearly random or left to right order my whole life, never had any kind of reaction to it.

@user91988: At age 65, having been brought up in a family of Boston Brahmins on one side, and southerners on the other, attending prep school and an ivy league college, I'm probably about as formal a person as you'll find. I know of no such rule for listing people unless, perhaps, they are otherwise undistinguishable. If I'm inviting my friend the senator, his daughter, and her friend, it'd be Senator Goodfamiliy, Martha, and Bitsy. Just the senator and wife, by mail? Sen. and Mrs. Goodfamily. But "Cousin Amelia, Senator, Mrs. Smith, will you join me on the porch?" if Amelia is 95 years old.

@jrh: For math papers, order is rather often alphabetical.

I would ignore all advice from anyone who is not personally familiar with the social conventions in Germany, and more particularly, in German academia.

@John Isn't it generally sorted by the importance of each individual contribution? For example if I publish something with my professor, it is usually me first if the paper presents some intermediate result of my thesis (I contributed more to the result). I've seen this in almost all math papers in my field that I've read so far.

@user91988 I'm going to chime in with the others and say I have never heard of this "rule" in English. As one of the other commenters suggested, I think you should provide a solid citation from an authoritative source (e.g. an English grammar book or some such), preferably a modern one. Or at the very least don't insist that it is definitely a rule if you are basing that on your own subjective experiences rather than an authority.

Sort-order for math papers: More modern papers may sort by importance. I think older ones tended to be alphabetical, esp. pre-1980 or so, which is when most of the papers I've read were published.

Dear both,?????

@AzorAhai--hehim US Department of State Protocol for the Modern Diplomat says "When making introductions, honor is recognized by the name spoken first. Courtesy gives honor to those who are older, higher in rank, titled, have a professional status, or are female." So yes, women first among equals. It's not surprising to find people who are ignorant of these rules of formal etiquette, they're mostly reserved for the dinner party crowd these days. And they have changed in recent decades, with many women preferring equal treatment

@AC Yes, I agree, it has changed and is no longer relevant to day-to-day life. Diplomatic protocol is not relevant to emailing professors in the US.