Imports github.com/sendgrid/sendgrid-go github.com/sendgrid/sendgrid-go/helpers/mail github.com/smtp2go-oss/smtp2go-go github.com/mailersend/mailersend-go github.com/mailjet/mailjet-apiv3-go/v4 github.com/malcolm-davis/go-stopwatch Standard library imports bytes context encoding/json errors fmt io log net/http strings time