Python-сообщество

 thr_lst = []
sem = threading.Semaphore(S_THREADS)
with sem:
    for ind, mail_to in enumerate(mail_list):
        if (ind != 0) and (ind % int(S_COUNTER_OF_SENT_EMAILS)) == 0:
            send_for_my_email()
        thr = threading.Thread(
            target=run_smtp_send,
            args=(mail_to,),
            daemon=True
        )
        thr_lst.append(thr)
        thr.start()
    [i_thr.join() for i_thr in thr_lst]