I set up a G Suite account for an organization's domain that I owned back when that was a free service. I'm effectively grandfathered in now for life; now Google refers to it as a "legacy G Suite account." For all intents and purposes it's just a regular G Suite account; I just don't get billed for it but I also get no support from Google.
Recently I noticed that my email address was no longer getting any emails. If I log into that account and send a message to myself, that is the only thing that works. Trying to email in from any other account at all results in a bounce back with this message:
530 SMTP authentication is required.
I have no idea how to troubleshoot this, frankly. This email address has worked for the longest time and this is only a recent result. I definitely haven't been fiddling with any settings so I'm not sure what change occurred on Google's end that would have brought this about. Any ideas on how to fix this, so I can start receiving email again?