Get only NEW Emails imaplib and python

Something like this will do the trick.

conn = imaplib.IMAP4_SSL(imap_server)

try:
    (retcode, capabilities) = conn.login(imap_user, imap_password)
except:
    print sys.exc_info()[1]
    sys.exit(1)

conn.select(readonly=1) # Select inbox or default namespace
(retcode, messages) = conn.search(None, '(UNSEEN)')
if retcode == 'OK':
    for num in messages[0].split(' '):
        print 'Processing :', message
        typ, data = conn.fetch(num,'(RFC822)')
        msg = email.message_from_string(data[0][1])
        typ, data = conn.store(num,'-FLAGS','\\Seen')
        if ret == 'OK':
            print data,'\n',30*'-'
            print msg

conn.close()

There's also a duplicate question here - Find new messages added to an imap mailbox since I last checked with python imaplib2?

Two useful functions for you to retrieve the body and attachments of the new message you detected (reference: How to fetch an email body using imaplib in python?) -

def getMsgs(servername="myimapserverfqdn"):
  usernm = getpass.getuser()
  passwd = getpass.getpass()
  subject = 'Your SSL Certificate'
  conn = imaplib.IMAP4_SSL(servername)
  conn.login(usernm,passwd)
  conn.select('Inbox')
  typ, data = conn.search(None,'(UNSEEN SUBJECT "%s")' % subject)
  for num in data[0].split():
    typ, data = conn.fetch(num,'(RFC822)')
    msg = email.message_from_string(data[0][1])
    typ, data = conn.store(num,'-FLAGS','\\Seen')
    yield msg

def getAttachment(msg,check):
  for part in msg.walk():
    if part.get_content_type() == 'application/octet-stream':
      if check(part.get_filename()):
        return part.get_payload(decode=1)

PS: If you pass by in 2020 after python 2.7 death: replace email.message_from_string(data[0][1]) with email.message_from_bytes(data[0][1])

The above answer does not actually work anymore or maybe never did but i modified it so it returns only unseen messages, it used to give : error cannot parse fetch command or something like that here is a working code :

mail = imaplib.IMAP4_SSL('imap.gmail.com')
(retcode, capabilities) = mail.login('email','pass')
mail.list()
mail.select('inbox')

n=0
(retcode, messages) = mail.search(None, '(UNSEEN)')
if retcode == 'OK':

   for num in messages[0].split() :
      print 'Processing '
      n=n+1
      typ, data = mail.fetch(num,'(RFC822)')
      for response_part in data:
         if isinstance(response_part, tuple):
             original = email.message_from_string(response_part[1])

             print original['From']
             print original['Subject']
             typ, data = mail.store(num,'+FLAGS','\\Seen')

print n

I think the error was coming from the messages[0].split(' ') but the above code should work fine.

Also, note the +FLAGS instead of -FLAGS which flags the message as read.

EDIT 2020: If you pass by in 2020 after python 2.7 death: replace email.message_from_string(data[0][1]) with email.message_from_bytes(data[0][1])