Some Gmail users who put the vacation auto-response feature to use, complain of encountering a ‘message blocked’ notification. The issue being reported is that the auto response fails to reach the target recipient. The account from which it was generated receives a notification instead, saying that the message is blocked.
This issue came to notice on February 27, 2017 when it was reported for the first time. Those who faced the issue note that when an email is sent to an account which has auto-response activated, the response is generated but blocked in between before reaching the actual recipient. Some of the users reported that the message was blocked due to the presence of one or more URL links within the content.
The screenshots shared by the users shows what messages they receive:
The troubled users got to hear from a Google Products expert on April 13, 2017.
“I am working with my team on this issue, I’ll get back to you with an update”.
She repeated the same on July 5, July 14 as well as on July 24. It likely that Google is aware and working on the issue, although the company is yet to officially acknowledge it. Meanwhile, here’s a suggested workaround, just in case you wanna try: Remove URL (links) from vacation responder and then send the email again.