I use a string (mangled here):

cat code.sh | mail -s "Code" me@my.net -r admin@remailer.net

to send code to myself to back the server code up to my local computer.

I run a remailer and found that the mail program began to refuse to mail one of my .sh files after I had made some additions and changes. I narrowed it down to one word (or IP address) in the .sh file that apparently causes mailx to refuse to send the mail.

The string that breaks mailx is hermetix.org .

Do you have blacklisting/whitelisting rules in your config? Which relay are you using Postfix/Sendmail?

If you telnet into the relay, and create the message by hand, what does the maillog say?

I am using Postfix/Sendmail. No blacklisting/whitelisting rules.

/var/log/mail.log records:

Oct 5 04:01:49 me postfix/smtpd[2271]: connect from unknown[204.101.75.250]
Oct 5 04:01:49 me postfix/smtpd[2271]: DCF89800C0: client=unknown[204.101.75.250]
Oct 5 04:01:50 me postfix/cleanup[2177]: DCF89800C0: message-id=<20141005035152.6ACD85C065@mail.hermetix.org>
Oct 5 04:01:50 me postfix/qmgr[2139]: DCF89800C0: from=<mixmaster@mail.hermetix.org>, size=29259, nrcpt=1 (queue active)
Oct 5 04:01:50 me postfix/smtpd[2271]: disconnect from unknown[204.101.75.250]
Oct 5 04:01:50 me postfix/local[2300]: DCF89800C0: to=<mix@me.net>, orig_to=<remailer@me.net>, relay=local, delay=0.37, delays=0.36/0/0/0.01, dsn=2.0.0, status=sent (delivered to command: procmail -a "$EXTENSION")
Oct 5 04:01:50 me postfix/qmgr[2139]: DCF89800C0: removed