error when sending mass contact

When I try to send a mass contact I get "1 errors encountered sending message. Please check the logs and try again".

I believe I have things configured correctly as I had it working in a previous ISP. I'm now working on Dreamhost. When I examine the logs this is what I find:

postdrop: warning: stdin: illegal length 5673, record type 78, referer: http://www.xxx.com/mass_contact
postdrop: fatal: uid=2639006: malformed input, referer: http://www.xxx.com/mass_contact
sendmail: warning: premature end-of-input on /usr/sbin/postdrop -r while reading input attribute name, referer: http://www.xxx.com/mass_contact
sendmail: fatal: xxxadmin(2639006): Error writing message file, referer: http://www.xxx.com/mass_contact

Any guidance will be most appreciated!