Fonte: https://support.plesk.com/hc/en-us/articles/4404507735826-Mail-client-provides-warnings-regarding-IMAP-connection-for-Plesk-mailboxes-inotify-initialization-error

Resolution

1. Connect to the server via SSH.
2. Check the current per-userid limit of inotify file descriptors:

   # cat /proc/sys/fs/inotify/max_user_instances
   128

3. Increase this value to a greater one via the command below, for example to 200:

   # echo “fs.inotify.max_user_instances=200” >> /etc/sysctl.conf

   Note: Rough metric is the number of concurrent IMAP sessions multiplied by 4.

4. Apply changes by executing the command:

   # sysctl -p

5. Restart Courier-Imap services:

   # systemctl restart courier*