chore(deps): bump github.com/emersion/go-smtp from 0.20.2 to 0.21.0 (#1888)

* chore(deps): bump github.com/emersion/go-smtp from 0.20.2 to 0.21.0

Bumps [github.com/emersion/go-smtp](https://github.com/emersion/go-smtp) from 0.20.2 to 0.21.0.
- [Release notes](https://github.com/emersion/go-smtp/releases)
- [Commits](https://github.com/emersion/go-smtp/compare/v0.20.2...v0.21.0)

---
updated-dependencies:
- dependency-name: github.com/emersion/go-smtp
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

* fix(reporter/email): use DialStartTLS instead of StartTLS

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: MaineK00n <mainek00n.1229@gmail.com>

config/smtpconf.go

@@ -9,6 +9,7 @@ import (
 type SMTPConf struct {
 	SMTPAddr              string   `toml:"smtpAddr,omitempty" json:"-"`
 	SMTPPort              string   `toml:"smtpPort,omitempty" valid:"port" json:"-"`
+	TLSMode               string   `toml:"tlsMode,omitempty" json:"-"`
 	TLSInsecureSkipVerify bool     `toml:"tlsInsecureSkipVerify,omitempty" json:"-"`
 	User                  string   `toml:"user,omitempty" json:"-"`
 	Password              string   `toml:"password,omitempty" json:"-"`
@@ -51,6 +52,11 @@ func (c *SMTPConf) Validate() (errs []error) {
 	if c.SMTPPort == "" {
 		errs = append(errs, xerrors.New("email.smtpPort must not be empty"))
 	}
+	switch c.TLSMode {
+	case "", "None", "STARTTLS", "SMTPS":
+	default:
+		errs = append(errs, xerrors.New(`email.tlsMode accepts ["", "None", "STARTTLS", "SMTPS"]`))
+	}
 	if len(c.To) == 0 {
 		errs = append(errs, xerrors.New("email.To required at least one address"))
 	}