Tell me what to send email in PHP

Also suggest swiftmailer using smtp. Architecture and code quality it is better than phpmailer'. Well documented. Extensible.
In General, if you use software distribution via smtp, the load and speed depends almost only from the postman and settings.
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For one project, swiftmailer successfully sends quite a bulk mailing via exim on a shared hosting.

Use swiftmailer with smtp transport. I can't complain.
Based on my limited experience, it is important: to form a queue and send it; use an existing box; write the correct headers.

It seems evil to NOT use the wonderful functions of SMTP.
Going to try with the SMTP enabled.

Use our own wrapper for mail () on the server side, as mailer is exim.
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Construct all subscribers, and letters sent portions, approximately 100 letters per minute, for the crown until you all go. Relazionati php a system is in principle quite simple.
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It is noticed that the server load itself is not sending messages, and the incoming stream of letters in response (subscribers — mostly various kinds of entities, and many have an answering machine "thank you, your letter is received," etc.) — this volume of letters processed spamassasin and loads the server. To these to fight just made to the box, which is mail that has not been tested SpamAssassin

also am using swiftmailer + exim — send out about 3000 notifications per day, there is no problem