Sharon Strauss

Actually, we may use Web Portal, but we call it HelpCenter....  I do not see any 'Do not reply' text in the mail notifications.

We use HelpCenter. 

I completely agree with Allison. Please enable the feature to respond via email.

I'm unsure if Peter is suggesting that the fact that users can reply to forum's via email is a bug or if he is suggesting that he does not like that replying to a forum topic via email creates a new ticket.  Maybe this should be a feature in which you allow your customers the ability to change the settings so that if we want them to be able to respond via email to a forum topic(this is my vote!), their response will be added to that topic(like they expect it too- and keep it consistent with the way they can respond to tickets via email and have their response is added to the ticket) or allow your customers to turn off the setting and instead have a message sent to them to inform them that they need to login in order to respond to the ticket. 
I agree with Dan: "Mark them up however you need to in order to associate them with a forum post and make it a consistent experience for your customers. The forums were one of the features we liked about Zendesk but this lack of consistency is not something we'd anticipated and it devalues the feature. You've got smart developers."  You can make this happen, you already have it coded for via email responses.

We would also love to see this feature supported.  A large portion of our tickets come in via email and most of the responses our customers send to the tickets are via email.  Not being able to respond to the forum requests in the same way as the tickets makes it confusing for the customers(having two sets of rules) and means they may be less likely to keep using the forums(not what we want to happen). 

Please update this functionality so that it is consistent throughout your application.  Thank you!