2020-02-19 12:06:20 1j4Snk-0004ii-37 Error while reading message with no usable sender address (R=1j4Snk-0004ig-1l): rejected by non-SMTP ACL: local configuration problem
2020-02-19 12:06:20 1j4Snk-0004ig-1l Child mail process returned status 1
Your information is too ambiguous, it is impossible to help you without knowing details. There might be numerous reasons with the same symptoms. Anyway try and
1. rebuild dovecot, and make sure it's running
2. make sure 25 port is opened for incoming emails
3. check MX records, and make sure they are fine
4. check disk quota and mail size of email boxes
5. make sure Local Mail delivery is enabled.