ok, if you do not have a static IPv4 allocated by Att, then please look into https://docs.cloudron.io/networking/#dynamic-dns and use a domain backend which is programmable (anything besides wildcard and manual)
Once that is configured, you can sync dns and your issues should be solved.
Further please note the port limitations on such ISP connections https://docs.cloudron.io/email/#smtp-status nearly always is outbound port 25 blocked on such connections, so you most likely have to use some email relay.