Index: imap.rb
===================================================================
--- imap.rb	(revision 655)
+++ imap.rb	(working copy)
@@ -228,10 +236,12 @@
         ## fails with a NO response, the client may try another", in
         ## practice it seems like they can also send a BAD response.
         begin
+          raise Net::IMAP::NoResponseError unless @imap.capability().member? "AUTH=CRAM-MD5"
           @imap.authenticate 'CRAM-MD5', @username, @password
         rescue Net::IMAP::BadResponseError, Net::IMAP::NoResponseError => e
           Redwood::log "CRAM-MD5 authentication failed: #{e.class}. Trying LOGIN auth..."
           begin
+            raise Net::IMAP::NoResponseError unless @imap.capability().member? "AUTH=LOGIN"
             @imap.authenticate 'LOGIN', @username, @password
           rescue Net::IMAP::BadResponseError, Net::IMAP::NoResponseError => e
             Redwood::log "LOGIN authentication failed: #{e.class}. Trying plain-text LOGIN..."