Send mails in background without cron

Question

I was wondering if there is a way to run a PHP loop in order to send a few hundred emails to subscribers in background. My goal is to format the newsletter, click send and then

Answer 1

I know this can be made with a cron job reading from a queue saved in MySQL or text file, but this way, even if there is no queue for a long period, the cron will always be running, looking for the queue...

That pretty much beats the purpose of Cron. You should create a job that runs, say, every 15 minutes and checks the queue for mails that need to be sent. If there are no mails, let the script die, it'll run again in 15 minutes.

If there are mails to be sent, update the rows to indicate that you're processing them before you start sending, so a run taking more than 15 minutes won't cause another script instance to send the same mails.