Godaddy SMTP server randomly rejects emails
I have a few websites that run Joomla and send some notification emails via Godaddy SMTP server smtpout.europe.secureserver.net. Godaddy only allows 250 SMTP relays per day for free, but for this particular purpose this was more than enough.
One day I noticed that I was not receiving all notification emails I was supposed to receive. First of all all I logged on to Joomla's administration panel and tried to send some test emails using Joomla's built-in Mass Mail functionality. Results were interesting - most of the time emails would go through, but around 30% of the time sending would fail with error: