LMAO! See #35345

//cc @brianteeman

Documentation: https://docs.joomla.org/J3.x:Plugin_Joomla_Update_Notification

"Quick Tips: To turn off Joomla! update email notifications simply disable the plugin."

Ah yes. I'll close this, but perhaps the best option would be to give the user a choice, e.g. every 24, 12, 6 hours or none.

Already is configurable! You can set the cache time out already.

How? It's not an option on the plugin. I'm looking at 3.10, BTW and not 4.0 at the moment.

In /administrator/index.php?option=com_config&view=component&component=com_installer by setting `Updates Caching (in hours)'.

Thanks. Presumably it will need re-doing after every update as it will get overwritten with every update.

It's saved in the database so no, it should persist

Thank you, both, @wojsmol and @PhilETaylor, I'll give it a go.

Hi. Adding the URL above to the domain returns a not found, so I went to cPanel in File Manager and navigated to domain > administrator > components > com_installer > config.xml and changing line 30 from
default="6"
to
default="24"
for one test domain and
default="1"
for another.

I've tried 24 and 1 as I'm not sure whether 24 means 24 x hourly cache or 1 x 24-hr cache.

Either way, it has made no difference. I'm still getting the emails for both sites every six hours.

@Scrabble96 URL posted in my previous comment correspond to Extensions > Manage > Updates > open Options > change Updates Caching (in hours) to fore example 12. This is update cache expiration time so 12 hours means that mail will be send 2 time a day.

Thank you. Found it. :-)