I had issues with sendmail a while ago. my guess is that your ISP’s IP address could be
                blocked and because of which the e-mails are not being sent. You can verify that with the following
                command. Make sure you run this command from action runner.
            sendmail -v "[email protected]" <<EOF
subject:"test subject"
from:"[email protected]"
Example Message
EOF 
            If your ISP’s address is blocked you should see something like this in the output since you have enabled
                the verbose mode
            
                050 >>> DATA
                    050 250 2.1.5 OK 18si14075339plg.91 - gsmtp
                    050 354 Go ahead 18si14075339plg.91 - gsmtp
                    050 >>> .
                    050 550-5.7.1 [49.207.200.40] The IP you’re using to send mail is not authorized to
                    050 550-5.7.1 send email directly to our servers. Please use the SMTP relay at your
                    050 550-5.7.1 service provider instead. Learn more at
                    050 550 5.7.1 https://support.google.com/mail/?p=NotAuthorizedError
                    18si14075339plg.91 - gsmtp
                    050 root@8f4830ad0a22… Connecting to local…
                    050 root@8f4830ad0a22… Sent
                    250 2.0.0 05OE85F2001748 Message accepted for delivery
                    [email protected]… Sent (05OE85F2001748 Message accepted for
                    delivery)
                    Closing connection to [127.0.0.1