Could somebody explain to me, why is PHP's mail function not suitable for sending mass emails? I'd like to understand this as deeply as possible - it would be really nice if someone trained in the arcane art of sending email through PHP could explain how all this works. Other online sources are welcome too!
From php.net:
It is worth noting that the mail() function is not suitable for larger volumes of email in a loop. This function opens and closes an SMTP socket for each email, which is not very efficient.
The link above specifies 2 alternatives however.