Cloudron + mail relay + Fritzbox = block Port 25 outbound

[necrevistonnezr]

For our German friends:

I might be stupid but never realized that there is a way to block port 25 outbound on the (rather simple featured) Fritz Box:

If you use an mail relay (as is recommended), you don't need port 25 open outbound, only inbound (in order to receive mail), see https://docs.cloudron.io/email/#firewall

The related port setting is not - as one would guess - under Internet > Permit Access
but rather under Internet > Filter > Lists > Global Filter Settings
--> Then activate Email filter over port 25

Afterwards, you're still able to receive mail (directly) and send mail (over the mail relay) but the outbound port 25 is blocked for other applications on the network.