Constants define how Newsletter behaves on specific cases which are usually not to be changed. But since WordPress works in very heterogeneous environments and sometime people have really particular needs, those constants can be redefined (at your own risk!).

Constants are defined using the PHP define(…) syntax and they can be set in your wp-config.php file before Newsletter is loaded. Newsletter takes care to check if a constant is already set.

Note: constants cannot be redefined so if you set them in the wrong way Newsletter cannot adjust things later!

A value for a constant can be set using:

define('CONSTANT_NAME', 'value');

Please, do not play with your wp-config.php if you’re unsure on how a PHP file can be edited. Anyway always keep a backup and be prepared to upload the copy if something goes wrong.


This is the folder where Newsletter saves internal logs. The log level can be set on main settings and, usually, a log file is generated for each different component or module. Log file names contains a secret token and are rotated monthly.

The folder name MUST NOT end with a slash.

The default value is wp-content/logs/newsletter. The folder is created if it is not present.


This constant (ranging from 0 to 4) forces the log level of Newsletter and is applied to all modules. The log level can be set on the main settings panel but that values is ignored if the constant is defined.


Can be used to set the license key instead to set it on the main settings. In the main settings the license key will be detected but not shown.


Since version 4.8.9.

If set to false blocks the internal image resize which generates pixel perfect images when adding them to your newsletter. When the feature is disabled, images are added to newsletters as loaded in the media library (could lead to not perfect message display on some email clients).

This options is available for who is storing the media outside the blog.


Be warned: do not ask for support if you change this value and you then have delivery issues. Changing this value does not make the delivery engine working better or the the (sometime problematic) WordPress scheduler to work smoothly.

This sets the interval in seconds of the internal delivery engine. It is set by default to 300 seconds. Some people experimented with a value of 60 seconds and setting up an adequate cron trigger to reduce the mail load on the SMTP server. It’s not for everyone!


It disables the addons (both free and commercial) update: no notification of update available will be shown. To update an addons it must be removed, downloaded from the account panel and reinstalled.


If set to true, it disables the admin side warning about the not working scheduler.

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