As nothing was change on Piwik side, maybe your server was updated in any way? Or are you using the SMTP settings to send emails? If so maybe your password changed?
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Hi,

I can confirm that the server was not updated by any chance. We are not using the SMTP settings as well, And this is not a password issue as we are using Single sign on and the issue exists in our test instance as well.

Regards,
Sobhika

By the way, could you please tell me why the issue is closed.

Maybe the mail server is now blocking those emails. Try to check if the server itself is triggered to send any mails, or try using the SMTP settings, to prove that it really doesn't work.
But as you wrote, that it was working till June, Piwik itself was able to send mail and also did it, right? As the software didn't change, I can't see a reason why it should be a bug in Piwik. Piwik 2.17. is available for a long time now, and we didn't receive any other bug reports regarding unsent mails and it was working on all our instances.
As Piwik 2.x is almost EOL, we highly recommend to update to Piwik 3.

Hi ,

There was one change which was happened just one day before this happened. We had set up a cronjob for auto archiving on May 31st.

Not to defend, but I see similar kind of issues here :
#11534
#8996

Regards

which command are you executing for the cronjob? core:archive normally executes the scheduled tasks. Maybe that isn't done in your case. Do you have the output of a cron?

@sgiehl ,

I could fix this issue in our test instance by setting up a secure mail relay through SMTP. We are using port as 25 and method as 'TLS'. But, unfortunately with the same settings, the email reports are throwing an error ' Unable to connect via TLS' in PIWIK production instance.

Could you please help me find out what is the issue here.

Sorry, I'm not very familiar with setting up SMTP. Did you try to connect to the SMTP using TLS with any other tool?