As well as a set of rules the PHP mailing lists have a set of etiquette that everyone should be aware of. They are 'etiquette' in the sense they are guidelines, rather than strict rules as to what is and isn't acceptable.
However if you want to contribute to PHP internals you should probably be aware of them.
The core issues that people new to PHP internals should bear in mind are that:
Until you understand enough of what is going on, then it's difficult to effectively contribute to PHP internals development.
It is quite easy for new comers to PHP internals to accidentally hinder the project by limiting how useful it is for people who are active PHP contributors, even though people just want to help.
In particular, if you haven't been around in the project to understand what is being discussed, then it's appropriate to only read the messages, rather than getting involved in every conversation.
Although it's great that people new to the PHP internals discussion have lots of energy to discuss things, the mailing list is a tool that aims to help the PHP core developers to coordinate their work.
If people new to PHP internals are sending many messages, it makes it harder for the people doing the work to develop PHP core to communicate effectively with each other.
The email mailing list is a different communication method that you may not be used to, particular if you haven't used other newsgroups before.
It is not a chatroom, where you are only talking to a few other people. The messages you send are sent to hundreds of people. When you read a message that you think you could reply to, it is appropriate for you to take your time to fully understand what the other person wrote, and to carefully craft a response that is easy to read.
Additionally, by replying quickly you may be 'jumping ahead' of someone who might be able to respond much more authoritatively, but who only reads the mailing list every evening, or every few days.
It's okay for messages to not be responded to for days.
So that they are easy to read, you should spend time carefully drafting your messages.
Messages that are longer than necessary can take up a lot of other people's time.
Also, the longer your message is, the less likely it is that other people will bother to read all of it.
If nothing else, if you are receiving an error message from the mail server that your message is too long, you should redraft it to be much shorter.
Trying to 'win' an argument by making an amusing word play is great fun....but it is not a good fit for messages that are sent to lots of people, particularly when not everyone on the list has English as their primary language.
Using the simplest and most direct words you can to express yourself will make it much easier for other people to read and understand your messages, which increases the chance your message will have a positive effect.
In addition to not 'top-posting' (i.e. please put your response below someone else's words you are quoting) cutting down a message you are replying to, so that you only quote the exact words you are replying to, makes it much easier for other people to understand what you are replying to.
A good rule of thumb is, there should not be more quoted text than new text, with an obvious exception for answering questions.
Not every conversation is going to result in a benefit to PHP. In particular, in situations where for many days a thread has only received messages from people new to PHP, and none of the core developers have participated, you should really be asking yourself "is keeping this thread active going to help the project?".