Email alert i/o timeout error dial tcp missing receiver missing group labels

I’m getting the following error when trying to send a Test email notification from my RHEL 8 (Linux) sever. Installed Prometheus and Grafana as services (instead of using Docker images) using YUM repository installation. Can someone please help?

This is the file path: /etc/grafana/grafana.ini
enabled = true
host = **:587
user = ****
password = *****
skip_verify = false
from_address = noreply@
from_name = Grafana

Tried with starttls = nostarttls option also in the same file but still getting the same error. t=2023-03-30T09:05:03.607196208-05:00 level=error msg=“Missing receiver” t=2023-03-30T09:05:03.607257464-05:00 level=error msg=“Missing group labels”
logger=alertmanager org=1 t=2023-03-30T09:05:12.375168702-05:00 level=error component=alertmanager orgID=1 component=dispatcher msg=“Notify for alerts failed” num_alerts=16 err=“Email Alerts/email[0]: notify retry canceled due to unrecoverable error after 1 attempts: failed to send notification to email addresses: dial tcp i/o timeout”
logger=context userId=1 orgId=1 uname=admin t=2023-03-30T09:05:13.608405778-05:00 level=info msg=“Request Completed” method=POST path=/api/alertmanager/grafana/config/api/v1/receivers/test status=408 remote_addr=xx.xx.xx.xx time_ms=10034 duration=10.034264628s size=500 referer=“http://xx.xx.xx.xx:3000/alerting/notifications/receivers/Email%20Alerts/edit?alertmanager=grafana” handler=/api/alertmanager/grafana/config/api/v1/receivers/test