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My SMTP server has sending limit up to 5 messages per second. On Drupal 6 site I have up to 500 users in organic groups to whom I would like to send newsletter.

What sending limit should I set for successful broadcast? Does Drupal send messages momentarily or during longer period?


I use Messages & Notifications modules which allow me to limit

  • number of messages
  • sending time in seconds
  • sending time in % of cron time

The only way to solve my problem I've found up to now is limiting the number of messages to 5 and setting cron to run every 15 minutes. But it is very sad to wait whole day to send about 500 messages.

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up vote 0 down vote accepted

If you start tracing from drupal_mail(), you will end up in the MailSystem. The DefaultMailSystem::mail() method sends out mail, unless another module has done otherwise. This hands off the email to the PHP mail() function, which does something system dependent.

As far as I been able to tell when I have debugged email problems, Drupal doesn't do any throttling. Typically, PHP doesn't throttle either. After that, it really varies and totally depends on the php.ini settings and other server setup.

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Thanks for the hint! But there is a way to limit sending mail - I use Messages & Notifications (updated question). – Vlad T. Dec 5 '12 at 17:09

I've had problems with mails not reaching a custom Google apps email address from the default mail function. Therefor I use SMTP module to handle my emails. It connects to every mail account(supports SMTP), and uses that to send a mail.

It works with Google Apps, and mail is sent instantly.

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I also use SMTP module, otherwise I wouldn't be able to send emails via SMTP. And I also used free Google Apps account, but it allows sending up to 500 messages per day. Recentrly I've subscribed to AWS SES account, but it has limitation of 5 emails/second. – Vlad T. Dec 5 '12 at 16:59

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