Well, it seems I've messed with Virtualmin in a wrong way. I am receiving the following message on the left hand column under the virtual server drop down list:
"Failed to query Postfix config command to get the current value of parameter recipient_bcc_maps:"
Everything was working okay until ... I'm not sure exactly. Here are a few things I did that I recall:
1) Deleted DNS records on the registrar side. For example, I removed CName "host" thinking it wasn't used. It turns out host.server.com is the default for webmin, as in "https://host.server.com:10000/". I don't know if host is used internally by Postfix or somewhere else, where the query failure would be affected. I did add the CName record "host" back though. Did not help.
2) I got this great idea of enabling "Sendmail Mail Server". It was in the "Un-used Modules" list. I'm not sure how to disable the server -- that is, move it back to the Un-used area -- so I'm not able to test if this is something that contributed to the error.
3) I added an FTP user to one of the domains served by Virtualmin the day before this occurred. I don't think this is a contributing issue though.
I've googled and read through other entries on this issue, but nothing has surfaced as the likely culprit.
Any ideas? Right now, I am still serving web sites, so Apache seems to be working fine. I'm able to SSH in as well.