Sendmail on a LAN

[Tim]

Tim:
>> Whether it be monthly, or more rapidly, SMTP servers aren't supposed to
>> change (numerical IP) addresses.  It's not a good idea to run a SMTP
>> server from a dynamic address.  When your address changes, you lose mail
>> (from anything that cached your IP, and keeps on using the cached
>> address), and someone else (who gets your old one) get spammed.

Ed Greshko:
> Actually, that shouldn't happen.  You may not get the email but it
> shouldn't get lost and the person that gets the previous IP address
> shouldn't get spammed.  I would expect the emails to be rejected with
> "User Unknown".

While the next person to get your IP mayn't actually receive mail,
they'll still get attempts to connect to their SMTP server, whether or
not they even have them, until other people's systems find out about
your new IP.

Now, if that person doesn't have a mail server, your second MX record
should be consulted by SMTP servers, and deliver your mail through that.
But, people doing the home SMTP game, probably don't have a second,
separate, SMTP server.  And those that do, will probably have to go to
that second server, deliberately, to get unreceived mail.  The second
mail server mayn't automatically pass the mail it's holding over to the
main one, when the main one does become available.

Long ago, I decided that trying to be my own SMTP server was too much
trouble to bother with.  You really want a static IP, that costs more.
You need to handle all the spam, that a dedicated mail host is much more
proficient at dealing with.  You really need a second backup server,
that costs more, and since that's external, why not have both external.

I settled for running my own server for our outgoing mail, and let my
domain's hosting equipment handling my incoming mail.