Reduce the size of the wp_mailpoet_scheduled_task_subscribers table.

You can reduce the size of this table by running the following SQL query:

DELETE FROM wp_mailpoet_scheduled_task_subscribers where created_at < ‘2019-01-01’;

Ensure to use the same table name as on your site and change the date to the desired one.

Also, I recommend creating a backup of your database before running it.

MailPoet Help: We use this table to track subscribers who you’re sending newsletters to. That is the main purpose of this table. When creating a newsletter, we insert a row for each subscriber to this table. When the sending for this subscriber is done, we mark the row as processed. After that, we use the data in this table for the inactive subscribers’ feature.

When we are looking if a subscriber is inactive, we look in this table. So if you are not using the inactive subscribers’ feature, you can delete any older processed data. If you are using the feature, you should keep the data for the period you set up in the settings`