I do not know how long ago it was, but some of my mail started to go
out without an envelop sender address. I've not yet been able to
figure why, but one thing I don't like is the appearance of my
/etc/resolv.conf file. It looks like this:

nameserver 192.168.254.254
search home
domain home

The 192.1683.254.254 is my router. I assume that "home' is useless.

I installed resolvcom, ran it with a -u option and rebooted. All
this did was to remove the domain line from resolv.conf.

How is resolv.conf supposed to get the name of my ISP? I suppose from
my router. The router knows what Frontier SSID it is using and the
connection type is DHCP via 802.1x. It says public LAN is disabled.
But it appends -16 to my host name. My mail problem may have
started when Frontier replaced my router.

I installed resolvcon, ran it and rebooted. All it did was to remove
the domain line.

It used to be that for both the search and domian lines was found the
name of my ISP (Frontier.com). This seemd to work.