CONTINUAL INTEGRATION

Problem scenario
You quickly set up an email server on a virtual machine in a public cloud. Some emails from the server are being received but some are not being received. What could be wrong?

Solution
1. If you are using Postfix, check the files in these locations:

/var/spool/postfix/private/bounce
/var/spool/postfix/bounce
/usr/lib/postfix/bounce

2. Look at the file /var/log/mail for clues about what could be wrong. If it is being written to (that is, if there is mail activity), you may want to make a copy of the file and delete that copy when you are done. When examining the file with vi, use this command:
:set ignorecase
Then you can use the forward slash "/" to search for patterns (e.g., "return", "fail", or "undeliverable"). In our experience the word "rejected" is a good one to search for.

3. Check the hostname of the server to see if it has numbers. The email server's hostname can be alphanumeric. Is an IP address visible (e.g., AWS servers look like this: 172-3-56-91.us-west-2.compute.amazonaws.com) in the hostname? Some spam filters will identify this hostname as a "likely spam" problem. There is a points algorithm that some anti-spam filters use which can lead to non-delivery of email. This can be solved as easily as changing the hostname of the server. Modify the /etc/hostname file to have the new hostname you want. Update the /etc/hosts file and mail.cf files to reflect this new hostname (without four octets being divided by dashes). Reboot the server and then send an email.

Please do not use this to spam people. Send email responsibly!

Another Possible Solution
Another way to do this is with Python; to learn how to use Python and not install anything else, see this external posting.

Problem scenario
You have a monitoring tool on a Linux server that needs to send out emails upon certain events happening. You want to install and configure an email server. You need to send outbound emails, but you do not need to receive inbound emails. How do you configure Linux SUSE to be able to send out regular emails over the internet?

Solution
1. Ensure that the security group allows for outbound connectivity over port 25.
2. Log into the Linux SUSE server.
3. Run this command: hostname

4. Ensure that the hostname does not have numeric sequences like an IP address. For example, the hostname should not have something like this (note the hyphens): ip-172-31-1-1

It seems unusual, but it bears repeating: you may encounter problems if the alphanumeric hostname has numeric sequences -- such are a tell-tale sign of an IP address. We have had problems with sequences of numbers in the hostname. To change the hostname, you would modify /etc/hostname so it has the hostname you want. Make sure that the /etc/hosts file has a stanza with the internal IP address of the server and the hostname in /etc/hostname. Once these are changed you should reboot the server.

5. Find the internal IP address. It is usually in the FQDN of an AWS server. You could run this command (and ignore the /20 at the end of its output):

ip addr show | grep eth0 | grep inet | awk '{print $2}'

You'll need the result of the above command later.

6. Run this command to install Postfix: sudo zypper -n install postfix

7. Edit the /etc/postfix/main.cf file.

7.a. The /etc/postfix/main.cf should have lines like these at the very end (but replace contint.com with the FQDN of the server 10.10.10.10 with the internal IP address as found in steps 3 and 4 above).

inet_interfaces = localhost, 10.10.10.10
inet_protocols = all
mydestination = $myhostname, localhost.$mydomain
myhostname = contint.com

7.b. In the /etc/postfix/main.cf, comment out the previous stanzas for inet_interfaces and myhostname in the file. Use the "#" (with no quotes) to do this. Save the changes.

8. If you have a DNS server so the FQDN resolves, skip this step. Otherwise update the /etc/hosts file to have an entry like this (where contint is the hostname in step 3 and where 10.10.10.10 is the internal IP address as found in step 4):

10.10.10.10 contint

9. Restart the postfix server. Run this command: sudo service postfix restart

10. Optional step. Test it. Type in the following but do these four things first to draft the commands specific to your environment: one, replace contint in the helo command with the plain hostname (the one that results from the "hostname" command); two, replace webmaster@contint.com with the sender's email address, or the one you want to appear as the sender; three, replace "goodperson@gyahoomail.com" with the destination email address, and four press enter after each line:

telnet 127.0.0.1 25
helo contint
mail from: webmaster@contint.com
rcpt to: goodperson@gyahoomail.com
DATA
This is just a test.
.
quit

An Alternative Way To Send Email
Another way to do this is with Python; to learn how to use Python and not install anything else, see this external posting.

Problem scenario
You want to search for activity associated with a given email address. You do not want to examine historical records because you made a configuration change. How do you eliminate the old records of the file and start over?

Solution
1. Make a back up of the file. (The commands below will eliminate the original copy.)
2. Run these four commands:

sudo su - 
cd /var/log
mail
exit