March 13th, 2017, 10:20 PM
It certainly looks like a craigslist issue from the text of the error message you received.
March 13th, 2017, 06:16 PM
That looks like the message is being generated by the craigslist e-mail server. It apparently does not like whatever you were sending if it is coming from gmail. You could try contacting craigslist...
March 13th, 2017, 03:38 PM
Things that might be helpful in diagnosing the issue:
A screen capture of the actual error message.
The domain you were sending the e-mail to (the part of the TO: e-mail address to the right of...