sendmail error

[Albert Cahalan]

I get error messages sent to the postmaster that contain this:

   ----- Transcript of session follows -----
554 MX list for zoomtel.com. points back to iota.zoomtel.com
554 <tonyf at zoomtel.com>... Local configuration error

Of course it points to iota.zoomtel.com, there is no zoomtel.com!
What is going on here?  This is what I have:

+-iota--------------------ISP------------------ The Net
|
+-epsilon
|
+-omega
|
+-gamma
|
+-alpha

All my machines on the left are connected by ethernet, and iota is
connected to the ISP via PPP every 20 minutes.  The ISP would call
iota zoom.zoomtel.com, and the windows PCs on the Ethernet would
call iota by number.

nslookup gives me this:

> iota
Server:  localhost
Address:  127.0.0.1
iota.zoomtel.com    preference = 5, mail exchanger = iota.zoomtel.com
zoomtel.com         nameserver = iota.zoomtel.com
iota.zoomtel.com    internet address = 192.168.0.18

> zoomtel.com
Server:  localhost
Address:  127.0.0.1
zoomtel.com         preference = 10, mail exchanger = iota.zoomtel.com
zoomtel.com         nameserver = iota.zoomtel.com
iota.zoomtel.com    internet address = 192.168.0.18

> epsilon
Server:  localhost
Address:  127.0.0.1
*** No mail exchanger (MX) records available for epsilon

> localhost
Server:  localhost
Address:  127.0.0.1
*** No mail exchanger (MX) records available for localhost