It happens time and again that a male colleague or student I never met writes me addressing me as “Madam” (or any other form of it). This is not a crime, but I wonder whether they are aware of what they are implicitly communicating by doing it, namely that they consider the fact of being a woman more relevant than the fact of being a scholar. Fine, if you are inviting someone to the opera, but somehow weird if you are asking them to review a book, write an article or participate in a conference…
I would therefore suggest to address members of the academia, if one is writing to them as members of the academia, by focusing on what makes them into members of the academia, namely their being scholars. This often translates into an academic title (Prof., Dr.…).
How do readers react when they are addressed in a different way?
At the start of each new year, my undergraduate students routinely ask me how they should address me. After blandishments about not caring, I usually suggest “Dr Wujastyk” or “Dr Dominik”. This week, several just called me “Professor” which is simple and pleasant. Of course, in the N. American context, that’s not such a complex title as in Europe; in that undergraduate usage, it just means “teacher.”
Some students email me starting, “Hey” or “Hi” without a name. They aren’t being rude – it’s just local friendly practice. But with my Euro-sensibilities I still find it startling every time. 🙂
An added layer of complexity is that in British English, a “Madam” is someone who owns a brothel. https://en.wikipedia.org/wiki/Madam#Other_usage
Turning to your actual point, I too sometimes get addressed by students (not colleagues so much) as “Mr Wujastyk”. I know it’s just inexperience and that no insult is intended. But of course in my case, as a member of the linguistically unmarked group, there are no subtexts about gender.
In Jnu, my students used to address me as “Ma’am” (pretty common distinction to Sir), in Vienna on the contrary I have to do google research to be sure not to offend my interlocutor by using the wrong academic title and write it fully, I would use Mr/Mme + last name for French professors, I usually very quickly end up with the first name of my North American, Israeli or Brazilian colleagues, regardless of tbeir academic title or gender… I thus always believed these practices were simply conventional academic practices that vary in different regions, which I have to learn to master to avoid further problems, rather than a gender issue. But of course, all of that is related (I would love to read a history of the use of academic title in Austria!). Anyway, I much enjoy the easiest first name option, but maybe because I don’t have enough title myself to enjoy a full ” Frau Prof. Dr.” and because my family name is the source of much trouble in pronounciation 😉