Should I setup a custom domain in Mailgun or use the given sandbox?

just wondering if I need to create a custom domain, since the info in the guide are missing and the interface is also changed.

if I am not required to do that, is there some advantage in doing that?

If you are using the sandbox from Mailgun every new member added in Ghost will be added to Mailgun, however you are required to verify each member by email. This means you need to go to your list in Mailgun, add the email to verify. The member then receives an email from Mailgun, needs to accept and only then can you send email campaigns from Ghost to the member.
If you upgrade and you’re not using the sandbox, you do not require to verify each member seperately.

I see that upgrading and having a custom domain are two different things. I can upgrade and keep using the sandbox, but for what you said it’d be stupid. Basically, if you want to use members it’s somehow “mandatory” to setup a custom domain in mailgun.

@sigul from what I understand, when using a custom domain, you cannot use a SMTP for bulk deliveries; hence the mailgun option. Or am I completely missing the point here?

You should not use sandbox domain for any real site. Sandbox are intended to test your software.

You should setup and use your own domain (“custom” as you described it).