[Bug fix] Unclear error message: Update users email via API (#36579)

- @noahtalerman: Tweak error message copy based on [@iansltx's
findings](https://github.com/fleetdm/fleet/issues/35145#issuecomment-3602600280).
- For the following bug:
  - https://github.com/fleetdm/fleet/issues/35145
- First PR:
  - https://github.com/fleetdm/fleet/pull/35581

server/fleet/emails.go

@@ -7,7 +7,7 @@ import (
 	"time"
 )
 
-var ErrPasswordResetNotConfigured = errors.New("Cannot send password reset. SMTP or SES Is not configured.")
+var ErrPasswordResetNotConfigured = errors.New("Cannot send password reset. Requires that SMTP or SES (email) is configured.")
 
 // Mailer is an email campaign
 // Types which implement the Campaign interface

server/mail/mail.go

@@ -95,7 +95,7 @@ func getFrom(e fleet.Email) (string, error) {
 
 func (m mailService) SendEmail(ctx context.Context, e fleet.Email) error {
 	if !e.SMTPSettings.SMTPConfigured {
-		return errors.New("requires that SMTP or SES is configured in order to send verification email")
+		return errors.New("requires that SMTP or SES (email) is configured.")
 	}
 	msg, err := getMessageBody(e, getFrom)
 	if err != nil {