Just as Mark notes - Pro plan expiry Is not disruptive. We know that all sorts of things can happen with billing and licensing, so we made sure to setup the system where if your Pro license is not active nothing changes on your site. The only thing that’ll happen is that our server won’t authorise download of paid apps updates via Studio. We have no control or access to clients SMTP settings or any other settings apart from updates authorisation that happens on our end via key/secret authentication based on oAuth.

Emails are sent by SMTP server - you can use included SMTP mailer app and send from the same server that your site is hosted on (UNA Cloud it your own) but this is generally going to send them all to spam folders, unless you diligently track all reports and communicate with spam tracker servers. Most active sites in the world, UNAbased or other types, use 3rd party mail sending services like Mandrill, AWS SNS, etc. They have special high-reputation servers that guarabtee 99% delivery and emails rarely route to spam. They charge for this service, because maintaining them is resource-intensive. Every time some Joe and Jill report your email as spam, spam trackers get alerted and handler of mail server has to handle the report or get banned. 

If your emails are not going through at all - spam folder or not, it means that either your own SMTP ain server is not configured properly or the 3rd party Smtp is not setup correctly.

Note, that even on UNA you only get a server and the site installation. We are not a mail-sending service and can’t guarantee delivery. Such service is typically charged for by volume, depends on nature of your emails, needs constant oversight and requires you to maintain integrity of your email opt-in settings.