Debian, minimum to send mail but not receive any

From Andreida

exim4

I tried sSMTP and nullmailer and both had their problems. Just install exim4 and be very careful to not allow any incoming mail, use /etc/aliases to forward everything to root and root to your external mail and it just works (for now).

sSMTP

After not being able to set the 'from' for mail from nullmailer, I tried sSMTP. Getting mails from 'root' is not really working if you have multiple server which send you mails.

  • install
apt-get install ssmtp
  • config in /etc/ssmtp/
    • ssmtp.conf
      • root=external-mail-address
      • mailhub=MAILSERVER-YOU-USE
      • #rewriteDomain=YOUR-DOMAIN.com (not so sure about this, I left it commented = disabled)
      • #hostname=<hostname> (should already be set, I disabled it for now)
  • revaliases
    • root:externalMailAddress:SMTP-Server


Set mailhub and you are good to go. 

echo 'This is a test!' | mail -s 'This is a subject' You@YourExternalMail.org

Now the correct 'full name' from /etc/passwd will be used. If you are getting mail from root, that is normal if you did not change that before :-) 

chfn -f 'root (Miracle Wiki Server)' root

Now you get mails from 'root (Miracle Wiki Server)' or 'root (backup-server)' which just makes so much more sense.

sending to root

echo test1 | mail -s test1 root

always gave me a relay error. I found out it takes the first entry after the external ip from /etc/hosts, adds it to root and uses that construct as new 'to'. Meaning I tried to send mail to 'root@backup' or 'root@backup.domain.de' depending on the sequence of the entries in the /etc/hosts file. I tried to use 'localhost' as first entry for the external ip which means it now looks like (x.x.x.x is an external ip like 123.22.33.56): 

127.0.0.1 localhost localhost.localdomain
x.x.x.x localhost host.domain.com host

This is probably VERY wrong, but it works. Now I can send mails to root and it tries to send to root@localhost and then /etc/ssmpt/revaliases is used and it then uses the correct target mail address. NO idea why that does not work for root@domain.com if it is in revaliases.


nullmailer

(source)

  • install
apt-get install nullmailer mailutils
  • Fully qualified domain name: yourCurrentServer (does NOT to have be fully qualified)
  • SMTP server: imap.yourdomain.com

It should work now, but you can tweak inside /etc/nullmailer/ the following files:

  • inside /etc/nullmailer
    • adminaddr - target mail (not understood yet by me, sorry; I think this should contain your normal external target email too. But I am guessing here!)
    • defaultdomain - source mail (so the sender not root@server but root@server.domain.com)
    • remotes - target login

from debian.org:

adminaddr If this file is not empty, all recipients to users at either "localhost" (the literal string) or the canonical host name (from /etc/mailname) are remapped to this address. This is provided to allow local daemons to be able to send email to "somebody@localhost" and have it go somewhere sensible instead of being bounced by your relay host. To send to multiple addresses, put them all on one line separated by a comma.

So far this works for mails to root@localhost. But as soon as the target is just "root", then it does not work any more. :-(

Good:

The original intend of this program has been reached, I can send to my external mail address without problems.
Example: 

echo 'This is a test!' | mail -s 'This is a subject' You@YourExternalMail.org

Not good:

  • mails to root (without @localhost) are not being send
  • outgoing mails have as sender 'root', no idea where to change this to give it a meaningful (server related) name
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