Sending email using netcat (nc) command

Sometimes you just have to send an email from a server you are currently working on, or you just need to test whether your email server is working, either way, you can always count on netcat to to the job for you. Below command will connect to the mail server you want, on port 25, and send email from there. Please take note, that this command is used in CentOS 7 server, using nmap-ncat-6.40-7.el7 package.

Connect to the mail.foo.bar on port 25

$ nc mail.foo.bar 25
220 mail.foo.bar ESMTP Postfix

Once connected, say hello to the email server

$ nc my.email.server 25 220 mail.foo.bar ESMTP Postfix

HELO foo.bar

250 mail.foo.bar

Specify a return address, just in case the email bounced. This is an SMTP protocol requirement.

$ nc my.email.server 25 220 mail.foo.bar ESMTP Postfix
HELO foo.bar 

250 mail.foo.bar 

MAIL FROM: mrbean@foo.bar 

250 2.1.0 Ok

Specify recipient of the email.

$ nc my.email.server 25 220 mail.foo.bar ESMTP Postfix
HELO foo.bar
250 mail.foo.bar 

MAIL FROM: mrbean@foo.bar 

250 2.1.0 Ok 

RCPT TO: teddy@foo.bar 

250 2.1.5 Ok

Put in you message (any message will do, but below is just how normal email usually formatted). Once you are done typing in your message, put dot (.) as a signal you are done with the DATA, and server will reply with your queue number.

$ nc my.email.server 25 220 mail.foo.bar ESMTP Postfix
HELO foo.bar
250 mail.foo.bar 

MAIL FROM: mrbean@foo.bar
250 2.1.0 Ok 

RCPT TO: teddy@foo.bar
250 2.1.5 Ok 

DATA
354 End data with .
From: mrbean@foo.bar
To: teddy@foo.bar
Subject: A gift
Date: Thu, 22 Mar 2018 12:00:00 +0000
This is merely a gift for you. Enjoy.
.
250 2.0.0 Ok: queued as 7F571241267C

To exit, just type quit, and you are done.

$ nc my.email.server 25 220 mail.foo.bar ESMTP Postfix
HELO foo.bar
250 mail.foo.bar 

MAIL FROM: mrbean@foo.bar
250 2.1.0 Ok 

RCPT TO: teddy@foo.bar
250 2.1.5 Ok 

DATA
354 End data with .
From: mrbean@foo.bar
To: teddy@foo.bar
Subject: A gift
Date: Thu, 22 Mar 2018 12:00:00 +0000
This is merely a gift for you. Enjoy.
.
250 2.0.0 Ok: queued as 7F571241267C 

QUIT
221 2.0.0 Bye

That's all,  the recipient should already received the email, or you should get a return email if it is bounced.

Check postfix email queue, and how to clear emails in there

To check the queue, we use a command called mailq, example as below:

$ mailq | tail

2024F98A61     3505 Mon Apr 27 18:16:17  support.us@something.com
(delivery temporarily suspended: Host or domain name not found. Name service error for name=smtp.something.com type=AAAA: Host not found)
                                         support.us@somethingelse.com
231EC98AED     3525 Fri Apr 24 16:48:04  support.us@something.com
(delivery temporarily suspended: Host or domain name not found. Name service error for name=smtp.something.com type=AAAA: Host not found)
                                         whoami@somethingelse.com

To clear the email in the queue, a command called postsuper is used, as below:

$ sudo postsuper -d ALL

To check the status of deletion, you can refer to the maillog, in below example, 15 messages have been deleted:

$ sudo tail /var/log/maillog

Apr 27 19:44:02 au-mel-rh-dev-3 postfix/smtp[6927]: 46F5598AF7: to=, relay=mta5.am0.yahoodns.net[98.138.112.37]:25, delay=2568, delays=2562/0.02/4.3/2, dsn=2.0.0, status=sent (250 ok dirdel)
Apr 27 19:44:02 au-mel-rh-dev-3 postfix/qmgr[5985]: 46F5598AF7: removed
Apr 27 19:44:04 au-mel-rh-dev-3 postfix/smtp[6925]: ABA8B98AFA: to=, relay=mta5.am0.yahoodns.net[98.138.112.34]:25, delay=1624, delays=1617/0.02/4.4/3.3, dsn=2.0.0, status=sent (250 ok dirdel)
Apr 27 19:44:04 au-mel-rh-dev-3 postfix/qmgr[5985]: ABA8B98AFA: removed
Apr 27 19:49:27 au-mel-rh-dev-3 postfix/postsuper[7913]: Deleted: 15 messages

Rebuild corrupted dbmail account

Symptoms of corrupted dbmail account are slow to open account and if manage to open account, it will take forever just to open the inbox. Here are the steps to rebuild back the account using joe's email account

1. You have to backup the the user's inbox. Use command "dbmail-export" to export mailbox to mbox file. For better management, export the mailbox to home folder.
# cd /home
# dbmail-export -u joe

2. A few mbox files will be generated depending on how many folders you have in your email. The mboxs will be placed in a folder named with your username, in this case, joe
#ls /home

3. Clear up the username mailbox using "dbmail-users". -e is for clearing mailbox
# dbmail-users -e joe

4. Delete the user. -d is for deleting user
# dbmail-users -d joe

5. Create back user. -a is for add user, -w for password, -p for password type and -s for aliases
# dbmail-users -a joe -w joe123456 -p md5 -s joe@example.com

6. Download dbmail tarball from here. Extract and you can see a script named mailbox2dbmail in contrib folder. Use that script to migrate back the mbox files to dbmail. For easy usage, copy the mailbox2dbmail script to /usr/local/bin. -u is for username, -t for type of input, -m for input filename and -b is for the name you want the mailbox to appear in your email
# cd /home/joe
# mailbox2dbmail -u joe -t mbox -m INBOX.mbox -b INBOX

7. Go to your joe's webmail and you can see the INBOX is already there. Repeat step 6 for all your mailboxes