At a point in my life when I was more or less in denial about being trans, one of my first jobs was in a call center. We were told to address people as 'Sir' or 'Madam' during training. After a while, I noticed a pattern. The male callers generally responded well to being called Sir. They liked it. However, female callers didn't respond particularly well to being called Madam. In general, they didn't seem to like it that much. I wondered whether terms Sir and Madam, which I personally think are quite old fashioned/arcane, conferred a perhaps more advanced age on the caller and the women didn't seem to like that much??? Or maybe the men seemed to like Sir because it conferred authority??? I'm stereotyping, but this was based on observation across thousands of calls I answered.
So after noticing this, I continued calling male callers 'Sir' but I found other ways to talk to the female callers, which they seemed to like better. Unfortunately, once you're using 'Sir' more or less exclusively, it gets easier to make the occasional mistake of calling women 'Sir' out of habit, particularly when you've been taking not stop calls for hours and your brain is going into melt-down. This was often sub-conscious and even happened when the caller obviously sounded stereotypically female. Time for very humble apologies, although it was possible to accidentally do this without even realising and occasionally I'd get called out.
The other thing that happened is I realised that a surprising number of people don't have voices that fit their gender stereotype. So it is possible to accidentally misgender someone, because their voice isn't in the typical range. Thats kind of a separate issue to what I detailed above. Anyway, despite what I'd been told to do, I more or less stopped using Sir or Madam unless it was absolutely 100% obvious who the caller was (eg they told me 'Hello I'm Mr Smith, and I wonder if you can help me with......').
I remember my first call from a trans person, a few weeks after I started. I mistakenly called her Sir. She rightly called me out and explained and I apologised. Later she complained to my supervisor, though I didn't face any disciplinary action because it was pretty much an unavoidable mistake on my part and besides, I'd been told by the company to address people as Sir or Madam.
Anyway, I guess what I'm trying to say is, it was not uncommon to for me to misgender people (and I'm trans) even when they were clearly sounded like their assigned or preferred gender. I did misgender a number of people, both trans and cis, but every single one was an accident and never deliberate or malicious in any way. That's not to say that some people don't deliberately misgender people (and that needs to change).
There was some discussion in training about the best ways to address people:
From what I can remember Sir and Madam were considered the safest. They said don't use ma'am as it is american and we were in the UK.
Alternatives included:
-Mr Smith/ Mrs Smith (still gendered and you needed to know the person's name which often you didn't learn until later in the call)
-First names (personally, I don't much like it when call center staff do this to me, it can sound really patronising and over-familiar)
- Love, Pet, Honey etc - Can get you in trouble, but some people can get away with using these to address others (Sadly, I'm not one of those people!)
Basically, I evolved my own system in which I just found ways to talk with people in a friendly, polite way without needing to use titles or names much.
They didn't cover much in the way of trans issues or anything gender-neutral, but this was 15 years ago.
Just thought I'd chip in as I've been on both sides of misgenderings quite a lot. And sincere apologies to all the people I misgendered over the years.