There is some confusion with users about replying, and email.
Posts in a category are arranged under a ‘topic’ - the first post on a subject. Using the web interface, hitting reply will make a new post under that same topic. The same applies to replies by email - they go to the right topic.
However, if you initiate a new topic by email, it will be submitted to the Category ‘General’. There is no way to choose the category for a new topic when using email (for very complex technical reasons). So if you want to start a new topic in a different category, just use the web interface. Go to the category and click New Topic.
Now more important than any of this - please don’t reply to a topic and change the subject. Pure havoc results - on almost any mailing list or forum. This is called thread hijacking, and it’s a perennial problem for admins. If you want to change the general subject or area of discussion in a topic, just make a new topic. This is very important so as to a) keep topics on subject, b) avoid messing up threaded email client views, c) help make topics readable by not confusing issues. It’s so important that a policy of this forum is that users who persistently hijack threads will be warned by moderators, with possible suspension if non compliant. So far we have avoided this!
And just as a reminder, please do read all the posts in this category, as there is a lot of useful information about how to use the forum here.