The Members page has recently changed, and there is no longer a link to managing email addresses on my hosted domain. I clicked around, and could find no resemblance of the feature. How does one manage their domain email addresses now?
The link to manage Domain Email should normally be under Email --> Domain Email Addresses. (You can also follow this direct link.)
It looks like one of your domains that has DNS hosted through another provider (GoDaddy) has stopped responding. The Domain Email Addresses tool attempts to check the MX records for each domain on your account to make sure they are pointing at Sonic -- if we don't get a response or they are pointed elsewhere, we omit the domain from available list as a safety precaution. I'd be happy to take a closer look once you have the DNS issue resolved.
-- Joe M
System Operations
Sonic.