i have 2 questions:
1. What is the difference between Rescan Headers and Get new Header?
2. Is it possible to resume downloads with server Y of files that you searched with server X without searching again?
Difference between Rescan and Get new Headers
rescan headers verifies the current header range in addition to downloading new headers (the latter is an option in properties->general, checked by default), since a server may delete or add (adding is less likely) headers in the middle.
to download from server Y when you searched server X just mark server Y as msg-id direct (properties->servers), you can set server priorities to define which server will be tried first.
to download from server Y when you searched server X just mark server Y as msg-id direct (properties->servers), you can set server priorities to define which server will be tried first.