Mail() vs SMTP?

[buileminh]

I dont know why I can not use mail() function on my hosting and I must use SMTP instead. I am wondering which use less server resource? I know for sending several emails, i would not care much about that but I am talking about sending hundreds, thousands or even more of email in short time (1 hours or can be 1 day). Which have more impact on server load/system performance? What is the best configuration for sending mail in that case?

--------------- Added [DATE]1232592873[/DATE] at [TIME]1232592873[/TIME] ---------------

Any help?

[buileminh]

Please help....

[Dismounted]

The mail() function calls Sendmail on the server, which sends the mail via SMTP (and opens a socket for each email). Using SMTP directly should be a little bit more efficient.