As discussed over a year ago, on December 21 the option to correspond about trademarks with the USPTO via paper mail will no longer be available. Instead, there will be the two electronic filing options (and TEAS RF will now be called TEAS Standard), and they will share an application form. The difference between them is based on how much of the administrative work the filer is willing to do; see your PTRC or this page for more details.
To incorporate these changes, TEAS and TEASi will be shut down on Saturday, December 21. Be prepared! Mandatory electronic filing is imminent.