How to organize a mass mailing list in php?

It is very important to hear the opinion of experts on the subject.
At first glance, the task is rather trivial, but it was not possible to go along with the sane detailed articles.

We have a VPS with a mail server and more than 1000 clients who need to send a newspaper in pdf with a size of 200 - 600 kilos. When using the phpmailer class, Mailer Error: Could not instantiate mail function crashes to more than half of the addresses . .

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