Which From/Reply-To addresses can I use?

ANSWER: When your community is set up in CONNECT, we ask for a domain that you would like to use for your email messages. This domain is setup in the backend by our Connect Support team so that you may set up any email address that uses that domain. For example: If the domain you ask to set up is "acmewidgets.com" then any email address that has that domain (ie. email@acmewidgets.com) will be valid for sending email.

However, this rule only applies to the From Address. The Reply-To address can be any valid email address from any domain and does not need to match the From Address. The Reply-To address is used when the recipient replies to your email message and is placed in the "To:" field instead of the From Address.