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Suddenly the e-mail function is not working anymore. In Joomla's global configuration when on SMTP throws the error SMTP Error: data not accepted. When on Sendmail option says: Could not execute: /usr/sbin/sendmail -t -i
Therefore, no e-mail can be sent anymore. I have checked everything, and tried with a fresh Joomla install, but there the e-mail works and messages are being sent.
Any ideas where the problem is?
I have my own dedicated server. After a week of investigations, it turns out i had the message_size_limit in Exim's configuration, the value set 1024 instead of 1024M so that emails were seen as too big. However, if I was using Joomla's default registration form, the activation email was sent, which makes it awkward. Perhaps message size was less than 1024KB :)