This is child plugin of parent plugin, Simple Email Queue, that provides capability to have limits for sent emails by giving options to set maximum number of emails sent in given period and having else put in queue.

This extension provides user interfaces so you can setup limits right from your WordPress admin.

It also enables queuing for any email sent from WordPress, not just one that is using custom function.

Using

First, you need to set what is maximum number of emails that can be sent in given period. By default, it sends 10 emails in 6 minutes. This means that if you want to send 15 emails in 6 minutes, only 10 emails are sent while rest 5 emails are put in queue and sent in the next period, after 6th minute has passed.

You can change this limit from your settings page.

Then you need to set period length where this limit of maximum number of sent emails applies. Please take care that this number is of seconds, not minutes (for example, if your period is 30 minutes, you would submit 1800.

This number can also be change from your settings page.

Different hosts use different limits. Please consult your host’s documentation or support to find this out. For example, SiteGround for its StartUp and GrowBig WordPress hosting plans is having a limit of 400 emails sent per hour (hover over “Email” row texts to find this out), while GoGeek is having a limit of 800 emails sent per hour.

All emails, sent are using built-in function wp_mail() or Simple Email Queue function simple_email_queue_add() are sent through queue, using limits. If you want to send email that doesn’t count in limits, you need to use method Simple_Email_Queue_Plus::get_instance()->wp_mail() in your code. This method accepts same parameters as function wp_mail().

Conflict

It is possible that other plugin that is loaded before Simple Email Queue Plus is defining function wp_mail() which prevents this plugin from sending emails using limits. If this is the case, you would get a warning in the admin header.

To workaround this issue you will need to stop using plugin completely or only that functionality, or to use function simple_email_queue_add(). It is not possible to use two or more plugins that define same function in the same time. This plugin tries very hard to prevent possible conflicts, but that is not possible in some cases or using some poorly coded plugins.

It is also that other plugin that is loaded after Simple Email Queue Plus is defining function wp_mail() in not safe way so you will get a fatal error. Same thing applies as above, but it says even more that other plugin is very insecurely coded.