(simple) campaign not sending mail after new user has been added

[EJL]

Check yourmautic/var/spool directory. If your messages are spooled there via queue refer to this

Hourly Limits

use –message-limit XX in your cron and replace the XX with the number of emails you want to send. If you are using queue then swiftmailer:spool:send --message-limit=xx specifies how many emails per cron are sent to your delivery server for processing (actual sending)