I've asked a similar question before now, but after a bit of a break, I've come back to the query and have also gotten a little further!
I can now successfully collect an email address from the body of the incoming email (using a regex

But, while I have hold of this address and can happily add it to a dynamic field, I can't find the right field to add the address as a customer email address. If I use OTRS-CustomerNumber it looks like it's going to work, but then when I hit reply from the ticket, it is still using the email address I sent the ticket from.
Can anyone advise?
Thanks a lot,
Scravid.