Hey Cristina,
You're totally right! There would be a middle step involved of adding the segment to a list first. Since you can't delete a segment directly from a list, you first select to add your segment to a list. There is a feature request regarding simplifying this process as well!
So from start to finish, your situation could look like: Add new contacts to new list, every six months pull a segment, add that segment to 'delete list', from contacts screen, remove everyone on the 'delete list' from your New list or Leads list. Afterwards, you could remove your 'delete list', as it was only serving the purpose of being able to pull this group of contacts off the Leads list. Hope this helps to clarify!
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