When checking my external mailbox from Yahoo Mail (classic and new beta), I get the error message that the LAST command is unsupported by the external POP server. How can I leave my mail on the server and download only the new mail ? I have no problem doing this with Gmail or Hotmail.

Yahoo has paid, trained TECHS who can help you with your question or problem. Make certain to go into much detail so they understand what information you need. (Simply copy and paste the question you've asked here into the form and add more details if necessary.)

Here's a link to a Yahoo! Mail Errors and Problems Reporting Form:
http://help.yahoo.com/l/us/yahoo/mail/yahoomail/bug_f.html?from_url=http://www.google.com/search?ie=UTF-8&oe=UTF-8&sourceid=navclient&gfns=1&q=yahoo+mail+help+fo rm

Here's a link to a Yahoo E-Mail Help Request Form:
http://help.yahoo.com/l/us/yahoo/mail/yahoomail/general_f.html?from_url=http://www.google.com/search?ie=UTF-8&oe=UTF-8&sourceid=navclient&gfns=1&q=yahoo+mail+help+fo rm

Use this form to report incidents of abuse or harassment.http://help.yahoo.com/l/us/yahoo/mail/yahoomail/forms_index.html