This is somehow started happening recently on some Joomla 3.6.5 sites.
Each time I save anything in the com_config - either on the global configuration, or a component's configuration, I am getting the notice:
You must provide at least one recipient email address
I can't find why I am getting this and not sure when exactly it started, but there was no change on any of the sites like changing the mail settings or similar.
Anyone has noticed that and have any idea what it is?
Hmm, I think I sorted out from where this notice is coming from. It looks like responsible for this is the latest version of Akeeba Admin Tools Pro (maybe it's also in the free core version don't know as I don't use that).
Admin Tools Pro v4.1.0 have some new features in its WAF configuration:
1. Monitor Global Configuration
When this is enabled and someone tries to change the Global Configuration of Joomla!, either from the back-end or the front-end, you will either be notified or they will get blocked (depending on your settings below).
2. Monitor Component Configuration
When this is enabled and someone tries to change the configuration of any core Joomla! or third party component (what you see when you click Options in a component's toolbar) from the back-end of your site you will either be notified or they will get blocked (depending on your settings below).
3. Action for configuration monitoring
What do you want to do when either global or component configuration is enabled and a change is detected in the configuration. 'Email' will simply send a warning email to the email addresses you've configured to receive security exception emails and only if you have configured such email addresses. The changes in configuration will go through. 'Block' will treat these changes as security exceptions. The changes in configuration will NOT go through.
This is actually the action that Admin Tools should do when something from the above 2 things happens. One of the options is to send an email.
So if any of the 1 and 2 features above is enabled and the email option is selected as action, but there is no email recipient configured to receive Admin Tools Security Exceptions, then each time someone saves anything in the Global or Component Configuration, Admin Tools will try to send an email but it won't have a recipient.