Troubleshooting Sendmail

Sometimes, you think you should be receiving email from your linux host but the email messages never come. You have verified the email address, you have installed different email program variants, sendmail, mail, mutt, etc…, and yet the messages still aren’t coming. I thought that in today’s article, I would share some troubleshooting tips to help you resolve sendmail sending issues.

Sendmail Not Sending – Verify That Postfix is Running

Sometimes, the reason that your messages are not arriving in your mailbox is simple, they may not be leaving the machine. Sendmail did its job and passed the message off to postfix, but if postfix isn’t running, then the messages will just be left sitting in the maildrop folder.  Check your postfix/maildrop directory for files.  If files are present, then postfix isn’t sending them and you know what the problem is.

Example: Below we see that lots of messages have queued up in the postfix/maildrop directory.

$ ls /var/spool/postfix/maildrop
01AA84B6E  1589A4B92  3377D4B91  51ACF48CC  6B9BF4B26  828514BB6  982C648D5  A8E9449C9  C03E24AC9  D871F4A4F
0368449DB  15E56485B  374964B78  537524B7A  6BF2349D0  
84D564B74  9907F48D3  AB1334AC8  C0F1D49CB  D893F4A39
039584B98  1728749AE  378464AEB  53C394B83  6C8204AE8  85200492A  992854AA4  AB2BB4A1B  C165F4ACD  D8A8E4A25
047A44A4C  17E7349EC  39017497A  55881492D  6CDE648B3  8595849E5  9A4434A49  AC3DA4ADD  C1BFE4A73  D955F4A1A
050D54A72  189E84A4E  3979D4A1D  563114AE4  6D32F48B6   982534A20  A87654B5B  BF4544952  D4DE64918

Now, let’s start up postfix and see if the messages get sent.  Be warned, you messages may have been building up for a long time and some very old messages may be about to be sent.  You may want to delete some of the older files if you want to prevent them from getting delivered.

Example: See if postfix is set to startup at machine boot

$ sudo chkconfig --list postfix
postfix 0:off 1:off 2:off 3:off 4:off 5:off 6:off

Well that explains it. postfix was not set to startup on boot. We will fix that.

$ sudo chkconfig postfix on

Now let’s start it up:

# service postfix start
Starting postfix: [ OK ]

That should send all of the email messages. Check your inbox and check the postfix/maildrop directory to verify that all of the files are gone:

$ ls /var/spool/postfix/maildrop

Sendmail Not Sending – Your IP Address is Blacklisted

Your email may be sending, but the recipient email address may be considering your messages to be spam based on the ipaddress or domain of your server.  You can check each of the typical spam blacklistings one at a time, or you can check them all at once using ( ).

Example – Checking Your Server’s IP Address for Blacklisting

You Can Check Your Server's IPAddress to See if it is Blacklisted

You Can Check Your Server’s IPAddress to See if it is Blacklisted


Browse to and check your domain and IP Address for listing.  If your address is listed, this is likely the reason that your messages are not arriving in your email inbox.


Check Your IPAddress to see if it is black listed

Check Your IPAddress to see if it is black listed



This address is listed!

Your address may be listed for many reasons, some of which are not your fault.  Each list has a method for removal, but if somehow your server is compromised, you may find that your address is relisted again unless you resolve the real issue.


Some lists (Example:  UCEPROTECTL1) will list you and state on their website that you can only petition them to remove your IP Address if you donate to their cause.  MXToolbox explains it this way:  This blacklist does support a manual request to remove, delist, or expedite your IP Address from their database upon Payment or Donation of fees to their organization.  (

I typically will not pay extortion fees like this.

Sendmail Not Working – Other Causes

There may be many other reasons why your email sent through sendmail is not getting delivered.  You may also want to check your spam folder in your email client, or verify that your Iptables firewall is not too aggressively set that messages don’t make it out.  You may have other reasons that you may want to add in the comments below.

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Jeff has 20 years of professional IT experience, having done nearly everything in his roles of IT consultant, Systems Integrator, Systems Engineer, CNOC Engineer, Systems Administrator, Network Systems Administrator, and IT Director. If there is one thing he knows for sure, it is that there is always a simple answer to every IT problem and that downtime begins with complexity. Seasoned IT professional by day, Jeff hopes to help other IT professionals by blogging about his experiences at night on his blog: You can find Jeff on or LinkedIn at: LinkedIn or Twitter at: Twitter

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