import re

def parse_command(cmd):
    result = []
    for part in re.split(rb'\s+', cmd):
        result.append(re.sub(rb'^(\w+)', lambda p: p[1].lower(), part).decode())
    
    return result

if __name__ == '__main__':
    print(parse_command(b'mail from:<hello@a.com> size=512 command=12'))
    print(parse_command(b'ehlo x.com'))