How to scedule a reminder mail for nodes with date field in an oganic group? I would like to enable all members of an organic group to subscribe to a reminder, that sends an e-mail depending on a date field.
To be more specific: The group has a group content with a date field. Now I would like a mail being sent a specific time before this date becomes actual.
Would would the best way to do this?
When it comes to right on schedule or specific time, you need to have crontab on server. Role of cron tab will be none other than calling your cron.php file which in turn allows all modules to set the cron. But this is half of the process since with core drupal cron process you can not have much control on setting schedule time, so you can use elysia cron module to extend drupal core cron.This was cron part

Now inorder to trigger email you can implement hook_cronapi() as an example,

function mymodule_cron_cronapi($op, $job = NULL) {  

  $items['send_email'] = array(
    'description' =&gt; 'Send email to group users',
    'rule' =&gt; '0 * * * *', // Every Hour at **:00
    'callback' =&gt; 'mymodule_email_group_callback',
  );
  return $items;
}


cron callback

function mymodule_email_group_callback() {
  // load all group content from that content type.
  // loop through all nodes check date
  // if true
  // get all subscribers and loop through them
  // send email
}