Email service, error unmarshaling JSON from secret

Same as #82

`error unmarshaling JSON: json: cannot unmarshal string into Go struct field EmailOptions.port of type int`

Start by reading issue #82 and tracing how the email service unmarshals its secret into EmailOptions, with particular attention to the port field. Reproduce the reported error using the secret format described there, then verify the supported representation and add or update coverage if the repository provides relevant tests. Done means the supported email secret no longer produces this unmarshaling error.

Written by the indexing model from the issue text.