You might receive an email that warns you about replying without changing the reply address.
That's because we use Amazon Web Services to send our emails. That's lower cost and more reliable than other methods, but AWS requires us to specify in advance which 'from' addresses it should accept. If, for example, a group leader sends you an email through the web site we normally have to change the 'from' address so it comes from firstname.lastname@example.org instead of their personal address. We then tell you that you shouldn't reply directly.
AWS accepts any address ending in @haylingu3a.org so there's no problem replying to messages coming from any of those addresses, and you don't see the warning.
When composing a reply, you can select the highlighted address in the warning message and paste it into the reply address. You can also right click the highlighted address, select 'Copy link' (or similar) and paste that into the reply address.
If you want to start a completely new conversation with the sender, you can normally click/tap the sender's name in the warning message.
Since we implemented the emailer, we've created some software that looks for responses made to the emailer (i.e. without changing the reply address). It tries to determine who you meant to reply to and, if it can, it forwards it on for you. Regardless, it sends you an email to explain what happened.