Client configuration guides

- iOS mobileconfig generator
- non-443 HTTPS ports in autoconfig etc.
- disabling POP service via SRV record
- fix display name in Outlook IMAP autodiscover
- allow multiple calls to TLSA generator and support Sieve STARTTLS

data/Dockerfiles/sogo/Dockerfile

@@ -8,6 +8,7 @@ ENV GOSU_VERSION 1.9
 # Prerequisites
 RUN apt-get update && apt-get install -y --no-install-recommends \
 		apt-transport-https \
+		bind9-host \
 		ca-certificates \
 		cron \
 		gnupg \