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.