Issues to sending email after full disk problem

Your software
My Mautic version is: 2.16.1
My PHP version is: 7.1.33

Your problem
My problem is:

After a problem with full disk server mautic is sending only a few emails per minute (via sendgrid API).

my spool folder has nearly 270748 and is increasing very fast.

These errors are showing in the log:

The mautic:emails:send shows me the following error message:

Type error: Argument 1 passed to MauticEmailBundleSwiftmailerTransportSendgridApiTransport::send() must implement interface Swift_Mime_Message, boolean given, called in /var/www/html/vendor/swiftmailer/swiftmailer/lib/classes/Swift/FileSpool.php on line 169

Steps I have tried to fix the problem:

Machine disk space is fixed, cleared the cache and updated mautic to version 2.16.1

Don’t know if you’re still having problems with this.

I got Swift errors like these on an SMTP route when authentication fails. Check your API settings.

You can try to run some some of the actions from the terminal to ensure email goes out faster to catch up. And you may need to adjust the frequency of sending mail or amount of mail you send in each batch.