If you have a large recipient list; e.g., thousands of email addresses, then sending a newsletter to them may require a long period of time, which may exceed the time limit set on the server for execution of PHP scripts. There are two methods of automatically resuming email campaigns to ensure that they are always completed in spite of server-side limitations: by means of the client (AJAX) script running in your browser and by means of a scheduler job (cron) set up on the server.
Method 1. Auto-resuming a campaign in a browser
The Mailer app opened in your browser is capable of automatically checking the current state of a running campaign and resuming it using until it is completed. To ensure that the message is sent to all selected recipients, it is sufficient simply not to close your browser tab with the opened Mailer app.
This method is not very reliable because the functioning of your browser may be affected by various force majeure factors; for example, you may accidentally open another app or website in the same browser tab, close the browser tab with the Mailer app, or turn off your computer if you forget to track the campaign completion progress. A campaign can also be interrupted if your Internet connection is broken.
To avoid the above-listed problems, use the second method.
Method 2. Auto-resuming a campaign by a cron job
For guaranteed completion of long campaigns it is recommended to set up two cron jobs: for sending the message to remaining recipients and for collecting and updating statistical information on the campaign-viewing page. Instructions on setting up these cron jobs are shown on the Send step if you never set up them before.