As of Laconica (now StatusNet) version 0.7 the email related settings are located in the upper right menu Account then follow the Email tab.
To post dents via email you have to create an incoming email address in your account settings. This address is automatically generated and not really easy to remember, so better put it in the address book.
Furthermore the address you are sending the dents with to this incoming address have to be the one you entered in your account settings. The check to prevent SPAM is case sensitive so watch out for upper and lower characters!
Posting dents via email works just as posting dents via the web interface. You can use all the tags and other features StatusNet offers.