alertmanager log: x509: certificate signed by unknown authority

[Zhaoyuan Zhang]

In alertmanager.yml,I tried

 smtp_require_tls: false in global and insecure_skip_verify: true in receivers,

both of them failed with:

level=error ts=2022-04-12T07:11:19.061Z 

caller=dispatch.go:354 

component=dispatcher 

msg="Notify for alerts failed" 

default/email[0]: notify retry canceled after 8 attempts: establish TLS connection to server: x509: certificate signed by unknown authority"

[Brian Candler]

There is a cryptic comment here:

  # The default SMTP TLS requirement.

  # Note that Go does not support unencrypted connections to remote SMTP endpoints.

  [ smtp_require_tls: <bool> | default = true ]

What I think it means is that Go does not support unencrypted SMTP connections with authentication.  There is more detail here:

https://github.com/prometheus/alertmanager/issues/1358

In other words: if you are using smtp_auth_username and smtp_auth_password, then in effect smtp_require_tls is forced to be True.