How best to reply (sub female)

Thank you all for the helpful feedback!

If in doubt ALWAYS Use their profile name.
It is the name they choose for themselves so it is the name they want to be called and you cant go wrong with it! if they wish other wise they should of named themselves that!
You can also ask what they wish to be called, after you figured out just why they have landed in your inbox. Like others have stated Someone needs to earn you calling them Sir/Master/Daddy don't just throw out the word to someone that doesn't deserve it. the word will loose its meaning.

In the Femdom (F/ffmm) world nothing annoys a Female Domme more than being called "Mistress" (Goddess etc) by someone that they don't own. .. Again profile name, we choose it, use it (although more often than not, those asking tributes will use it as a title. Report them if they do) Most males Dom are often the same as Dommes and don't wish an honorific unless they earnt that respect or you belong to them.

If you ask what they wish to be called, it also gives you time to assess what kind of person they are and opens the door to more conversation too!

Just for skimming and reading a few comments I think this has been said. But personally for me, no. If we had just started talking for example, don’t call me your dom referring to me as sir, master etc etc. The same way a dom has to earn his sub (I.e. I need to earn your submission), the sub has to earn their dom (I.e. sub has to earn the others dominance). To me there is nothing more aggravating than talking to someone and them immediately referring to me as sir or master etc. Personally that tells me they are just wanting to hop around. Then again, my view is shared with flash (my live in sub). We take those names seriously, we both have earned each others dominance and submission, and we take a dynamic and the accoutrements of that very seriously. Same with collaring. Training collar, day collar, and permanent collar eventually. But, we also are for the connection. We took the time to be friends first.

There is a huge misconception that bdsm and dynamics is just kinky sex and a little deeper level of trust to bring people together. It’s way more than that. I’ll let you do your own research but in my 2 years and now some personal experience, I’ve found the recurring study that couples who engage in bdsm and have a closer connection with eachother, stay together longer (lower divorce stats), and are generally happier than vanilla.

That’s my 2 cents

In the end it's up to the preferences of the individual. Aside from site terms-of-service rules, there's no official book of regulations on how, or even if, one should address one who messages them.

I'm a newbie Dom. But I personally feel that referring to all Doms as sir, without ever meeting them, kinda cheapens the term. Perhaps referring to Doms that you have met, and respect , as Sir, seems reasonable however.

"... depending on how your were raised ..."

This is a great statement add on to the conversation. Thank you!

You are not in any negotiated agreement. Until that happens no honorifics.

So I had a Dom message me, I responded and in his next message he asked that I call him Sir from then on. Would that be a red flag? I'm very new to all this.

Has he been Knighted by Her Majesty the Queen?

If not, only call someone "Sir" when you feel like doing so.

I don't call anyone sir unless I'm referring to MY Sir. I am polite/respectful (unless they are a d-bag right out of the gate), but I don't owe them any superlatives or honorifics.