Send user digests - Moodle task fails - sends hundreds of emails to Admin

On one of our Moodle instances, emails are supposed to go out through Google Workspace using Google SMTP servers. That being the case, we can't send an unlimited number of emails. So, email notifications had been globally - Site Administration > General > Messaging > Notification settings, which is located at server.url/admin/message.php

When there was a request to allow emails of a particular type to particular users, after enabling the email notification plugin at the above page, the next time a forum post was made, there was a cascade of Send user digests failed and Send user notifications failed messages.

For the immediate failure messages to stop, deleted all the adhoc tasks from mod_forum,

delete from prefix_task_adhoc  where prefix_task_adhoc.component = 'mod_forum';

I had previously set emailstop=1 on the database users table, for all users except the handful which should receive emails. Possibly the reason for the failures was that forcesubscribe=1 was set for many forums for many / all users. 

So, now I set it to zero (email disabled) for all forums on this instance, with

update prefix_forum set prefix_forum.forcesubscribe = 0;

and also updated the defaults,

Site administration > plugins > plugins overview > (chose mod_forum) > settings >

site.url/admin/settings.php?section=modsettingforum

and set subscription mode = subscription disabled for both defaults,

forum_announcementsubscription

and

forum_subscription 

Also, went to prefix_forum_subscriptions table and deleted all entries - which I suppose would be various users' subscriptions to various forums.

Hopefully this is sufficient to prevent the hundreds of failed send notification tasks. 

Update 13 Nov - Again received hundreds of task failed messages. Asked Claude.ai, and made the following changes as suggested, in addition to the above.

# Individual discussion subscriptions might still exist
DELETE FROM prefix_forum_digests;
DELETE FROM prefix_forum_discussion_subs;

UPDATE prefix_user SET maildigest = 0 WHERE emailstop = 1;

# Users might be getting auto-subscribed when they post
UPDATE prefix_forum SET trackingtype = 0;

TRUNCATE prefix_forum_track_prefs;