I've setup postfix as smarthost with different relayhosts and sender dependant authentication. Everything works ok, but I have a performance question. Is it better to send all the email corresponding to a domain through only one account? I mean, now I'm sending each message authenticating to the relay host with the sender credentials. Example: If I have 5 email accounts and I send 10 simultaneous messages from each account, How many times is postfix login to the relay host if I have sender dependant authentication? 5 times? once for each sender 50 times? once for each message If I send all the messages corresponding to one realy host through one account, how many times does postfix login to the relay host? only once? Thanks in advance.