I've had a cronjob working for about a fortnight without any problems. Then last night I checked I didn't get the email that I usually get. I went to the terminal to try send myself an email, I got the following error:

mail: cannot send message: process exited with a non-zero status

I haven't changed anything with my ssmtp cfg file. It just stopped working, when I check and recheck everything, the code, ssmtp, everything is perfect.

I send out my emails twice a day via cronjob. The crontab hasn't been interfered either. I really don't know why it would stop working.

The system sends out emails via gmail - I've gone into the gmail account and sent out test emails, they are sent and received without any problems.

Additionally I've checked throughout google, forums, websites I don't see any mistakes. This makes sense as everything was working fine 24 hours ago, and now it's just stopped.

Q: Is there any way of diagnosing and troubleshooting how to solve such a problem?

  • 1
    1) Have you tried running that cron command in your usual terminal to see the output? 2) Have you checked logs (usually in /var/log) 3) Have you checked that network ports used for mailing are not blocked on your Internet connection? Commented Feb 18, 2015 at 1:08
  • Q1 Yes, I did. When I did it gave the error. Q2 Looked at the /var/log, couldn't see any problems Q3 I've tried sending mail, from home, from thethering with my cell phone, and also from work - each of them have different internet connection - and all resulted with the error in the title.
    – 3kstc
    Commented Feb 18, 2015 at 1:18
  • 1
    What logs exactly did you check? Commented Feb 18, 2015 at 1:20
  • var/log/sudo syslog - it looks fine.. seems everything is working like crock work and then it started working again, I can send emails out from the terminal now....
    – 3kstc
    Commented Feb 18, 2015 at 21:47
  • 3
    /var/log/mail.log I guess Commented Feb 20, 2015 at 1:20

9 Answers 9


I have get the same problem in an Ubuntu 14.04 server. And I find error message in /var/log/mail.err, which said:

postfix/sendmail[27115]: fatal: open /etc/postfix/main.cf: No such file or directory

Then I just reconfigured postfix and solved this problem.

sudo dpkg-reconfigure postfix
  • 4
    Could you tell us what reconfig option you selected?
    – Fernando
    Commented Sep 6, 2015 at 14:29
  • 2
    I selected server as "internet server" and domain as server domain all rest were first choice. This worked for me. Commented Aug 16, 2016 at 15:24
  • 2
    thanks for the hint: /var/log/mail.err - big help for newbie
    – bkwdesign
    Commented Aug 18, 2020 at 3:43

Its mainly due to file size is very large, You can zip the file and resend them..


On Debian I got the error

mail: cannot send message: process exited with a non-zero status error 

and an exit code of

$ echo $?
$ 36

because the hostname in /etc/hostname and the name for in /etc/hosts differed.


I don't know if it helps to anyone, but here is my experience. I configure ssmtp just to send emails from my Ubuntu 18.04 server.

What cause me the error was that gmail had "less secure apps off", this caused that google couldn't authenticate my server's certificate. Once enabled, I could start sending emails from the server. Hope it helps!

  • Thing to note for all future viewers; Less Secure Apps will be blocked/disabled permanently from 15 feb 2021.
    – Asitis
    Commented Feb 3, 2021 at 12:52
sudo dpkg-reconfigure postfix

system mail name.

please read the log : vim /var/log/mail.err

ff@ubuntu:/var/log$ head -n 20 mail.err 
Sep  7 10:36:39 ubuntu sm-msp-queue[6302]: unable to qualify my own domain name 
(ubuntu) -- using short name
  • 3
    Can you spell this out a bit more? It starts with roaima’s answer but I don’t understand the next three words.
    – Jeff Schaller
    Commented Sep 7, 2018 at 10:05

I had the same error. I was using a gmail account to send emails. After checking my gmail I notice Google was sending to me Critical security alerts via email. I had to give permissions to unsecure apps in my Google account security section to make it works.

I'm using Docker and I have to implement the following in my Dockerfile too:

RUN echo "localhost localhost.localdomain" >> /etc/hosts

What caused me the error was that gmail had "less secure apps" set as "off", this caused google to be unable to authenticate my server's certificate. Once enabled, I could start sending emails from the server.

Go to your google account and search for "less secure apps" turn it on and test again! Worked like a charm from then on...


Sorry this is so simple, but fought this error for hours and nothing worked. But a simple uninstall and reinstall did.

I copied out my config files for reference and ran WARNING - the purge will delete your config files

sudo apt purge postfix


It reinstalled and ran without issue

  • As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.
    – Community Bot
    Commented Mar 23, 2023 at 14:45

The solution was on my Debian is run the mail command as root.

Login as root

sudo su

or send mail as root

echo "Test message" | sudo mail -s "Subject" [email protected]
  • 3
    Your second command runs echo as root, it does not send mail as root. Regardless, running something as root isn't really a solution, it just shows that you have permission issues somewhere. Commented Dec 15, 2020 at 10:31

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