StartTLSPolicy type
The StartTLSPolicy setting of the SMTP configuration
https://pkg.go.dev/github.com/go-mail/mail#StartTLSPolicy
KnownStartTLSPolicy can be used interchangeably with StartTLSPolicy,
this enum contains the known values that the service supports.
Known values supported by the service
OpportunisticStartTLS
MandatoryStartTLS
NoStartTLS
type StartTLSPolicy = string