From the [Deployment Guide][https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/pdf/deployment_guide/red_hat_enterprise_linux-6-deployment_guide-en-us.pdf]: Show
Email ProtocolsFrom the same guide:
Mail Transport ProtocolsFrom the above guide:
SMTPFrom the Deployment Guide:
Mail Access ProtocolsFrom the same guide:
POPOnto POP:
IMAPAnd here is IMAP:
Email Program ClassificationsFrom the Deployment Guide:
Mail Transport AgentFrom the same guide:
Mail Delivery AgentFrom the above guide:
Mail User AgentFrom the Deployment Guide.
Mail Transport AgentsFrom the same guide:
PostfixFrom the Deployment Guide:
The Default Postfix InstallationFrom the same guide:
Basic Postfix ConfigurationFrom the Deployment Guide:
Postfix ExampleSo let’s go ahead and try this out.Since postfix is the default MTA on RH6, let’s confirm it’s installed, set as the default MTA, and running:
Here is the default configuration:
Looks like be default local delivery should be working, so let’s install an MUA (mail) which in some cases can also act as a MDA/LDA (Mail/Local Delivery Agent):
Now from the root user let’s send an email to user1:
Now let’s switch user to user1, and see if the email is there:
So (as user1) I checked my mail queue, read the message, and then deleted the message. Now let’s try a remote delivery. First let’s configure an MX record for our domain, so we know which server handles our mail delivery. I added the following to my zone file:
I then restarted named:
then from the RH5, machine I was able to get the correct response back:
Now let’s modify the postfix configuration to allow for remote mail. Here is how my main.cf file looked like after the changes:
We can also use the postconf to list all the configured variables:
Now let’s check to make sure the configuration is okay:
Lastly let’s restart the service:
Now let’s open up the firewall:
Now from the RH5 client, let’s send an email from user2 to user1 to the remote machine:
Then on the mail server, check to see if that user has the mail:
On the RH5, machine we will see the following in the maillog file:
So basically the local MTA (sendmail, the default on RH5) accepted the message and then forwarded/relayed it to the RH6 machine, which is the destination Email Server. Then on the postfix RH6 machine, I saw the following:
We can also do a direct connection to the postfix server and send a message with telnet:
Then on the RH6 machine (as user1) we can check the mail:
If the mail queue gets stuck you can run the following to check the status:
If those are unwanted messages, just run the following to clean up the queue:
DovecotFrom the Deployment Guide:
Dovecot ExampleSo let’s try setting up an IMAP and IMAPS mail server. First let’s install dovecot:
Here is the default configuration:
Most of the configurations are under /etc/dovecot/conf.d. Here all the configurations:
Nothing crazy, we can see that the authentication is set as plain. We could use a user database for authentication, but it doesn’t look like we are using it. Then there are protocol specific stuff (imap and pop3). So under the main configuration let’s enable IMAP and IMAPS. Here is the configuration after I was done:
I also edited the /etc/dovecot/conf.d/10-mail.conf and specified the mail location:
As a test, I disabled SSL just to get plain IMAP working first:
Lastly I had to allow plain text authentication (we will disable this later):
You can get a summary of the enabled configuration by using doveconf:
Now let’s start it up:
In the log we will see the following:
Now let’s open up the IMAP port on the firewall:
Now on RH5 machine, run the following to check the email:
When I connected the first time, I saw the following error on the dovecot server:
Had to set the following in the /etc/dovecot/10-mail.conf:
After that, mutt showed me the following: Here is the connection to IMAP with telnet:
On the IMAP server, we will see the cache for dovecot:
Dovecot SSL ExampleNow let’s enable SSL for IMAP. First let’s create the Self Signed SSl certificate. This is done by editing the /etc/pki/dovecot/dovecot-openssl.cnf file and fill in all the information about your organization. Here was the default file from the install:
Here is all the information that I changed:
Now let’s backup the original certificate files:
Finally let’s create the certificate:
Now let’s enable SSL:
let’s also disable the plain authenticate without SSL:
Here are the non-default configurations:
Notice the SSL stuff (other than the certificates) is not here. This is because SSL is enabled by default. dovecot -a shows all the configurations, but it’s too much information. Here is the related information to SSL:
If you don’t want to restart the whole daemon, we can run the following to reload the configuration without restarting the daemon:
The logs, should show the following:
Lastly we can make sure, the daemon is listening on 993:
And of course let’s open up the firewall:
Running the following on the RH5 machine:
and I saw the following warning: After accepting the certificate, I saw my INBOX over IMAPS: Here is the connection to the IMAP server over SSL with the openssl command:
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Which of the following commands can be used to view the last 15 lines of a file select all answers that apply?Which command is used to combine three files into a fourth file? ... . Which of the following commands can be used to view the last 15 linesof a file (Select all answers that apply)?Ans:tail -15 some_filetail -n15 some_file.. Which of the following describes things Pstree can display?The pstree command displays the running processes in the form of a tree structure.
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