[Dovecot] Dovecot LDA and address extensions - folders flood

Hi list,

This post is slightly OT, I hope no one will take offense. I was following the wiki on using dovecot LDA with postfix and implemented, for our future mail server, the address extensions mechanism: an email sent to "validUser+foldername@mydomain.com" will have dovecot-lda automagically create and subscribe the "foldername" folder. With some basic scripting I was able to create hundreds of folders in a few seconds. So my question is how do you implement this great feature in a secure way so that funny random people out there cant flood your mailbox with gigatons of folder.

Thanks, kfx