When I Reply To A Job In Craigslist They Bounce Back

When i reply to jobs on craigslist, they bounce back. I log on to my mac thru icloud because i cannot access my emails directly [another story] and when i reply to jobs the bounce back message. below is what the message says. I am so frustrated and want to reply to these jobs I hv copy pasted in a new message also doesntwork.I have attached pdf docs etc but I dont think tht is the reason. Please advise…

Your message is being returned; it has been enqueued and undeliverable for
4 days to the following recipients:

Recipient address: 78ngn-2900541711@job.craigslist.org
Reason: unable to deliver this message after 4 days

Delivery attempt history for your mail:

Sun, 18 Mar 2012 22:36:29 +0000 (GMT)
Error reading SMTP packet; response to dot-stuffed message expected; likely problem with network or remote SMTP server

Sun, 18 Mar 2012 14:35:27 +0000 (GMT)