How mutt check to download emails from an imap server without downloading them more than once?

[Peng Yu]

Hi,

I use the following python code to download UNDELETED messages. But it
will fetch all messages without considering whether an message has
been downloaded previously. How does mutt solve this problem to only
download the emails that have not been downloaded before.

import email
with IMAPClient(host=host) as client:
  client.login(user, passwd)
  client.select_folder('INBOX', readonly=True) # preserve the \Recent flag.
  messages = client.search(search_criteria) # UNDELETED
  response = client.fetch(messages, ['RFC822'])
  for message_id, data in response.items():
    with open('%s/%d.eml' % (outdir, message_id), 'wb') as f:
      f.write(data[b'RFC822'])

-- 
Regards,
Peng