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](emersion/go-smtp@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>

go.mod

@@ -4,7 +4,7 @@ go 1.19
 
 require (
 	github.com/DusanKasan/parsemail v1.2.0
-	github.com/emersion/go-smtp v0.20.2
+	github.com/emersion/go-smtp v0.21.0
 	github.com/inconshreveable/log15 v3.0.0-testing.5+incompatible
 )
 

go.sum

@@ -2,8 +2,8 @@ github.com/DusanKasan/parsemail v1.2.0 h1:CrzTL1nuPLxB41aO4zE/Tzc9GVD8jjifUftlbT
 github.com/DusanKasan/parsemail v1.2.0/go.mod h1:B9lfMbpVe4DMqPImAOCGti7KEwasnRTrKKn66iQefVs=
 github.com/emersion/go-sasl v0.0.0-20200509203442-7bfe0ed36a21 h1:OJyUGMJTzHTd1XQp98QTaHernxMYzRaOasRir9hUlFQ=
 github.com/emersion/go-sasl v0.0.0-20200509203442-7bfe0ed36a21/go.mod h1:iL2twTeMvZnrg54ZoPDNfJaJaqy0xIQFuBdrLsmspwQ=
-github.com/emersion/go-smtp v0.20.2 h1:peX42Qnh5Q0q3vrAnRy43R/JwTnnv75AebxbkTL7Ia4=
-github.com/emersion/go-smtp v0.20.2/go.mod h1:qm27SGYgoIPRot6ubfQ/GpiPy/g3PaZAVRxiO/sDUgQ=
+github.com/emersion/go-smtp v0.21.0 h1:ZDZmX9aFUuPlD1lpoT0nC/nozZuIkSCyQIyxdijjCy0=
+github.com/emersion/go-smtp v0.21.0/go.mod h1:qm27SGYgoIPRot6ubfQ/GpiPy/g3PaZAVRxiO/sDUgQ=
 github.com/go-stack/stack v1.8.1 h1:ntEHSVwIt7PNXNpgPmVfMrNhLtgjlmnZha2kOpuRiDw=
 github.com/go-stack/stack v1.8.1/go.mod h1:dcoOX6HbPZSZptuspn9bctJ+N/CnF5gGygcUP3XYfe4=
 github.com/inconshreveable/log15 v3.0.0-testing.5+incompatible h1:VryeOTiaZfAzwx8xBcID1KlJCeoWSIpsNbSk+/D2LNk=