I doubt it is some specific part of the e-mail but rather the size of the e-mail. If the e-mail is short enough, then more will happen to read all of it (due to the buffer size it uses, etc.) before it decides to prompt you for the next screen. Then more closing the pipe doesn't cause a broken pipe.

The "broken pipe" message is harmless in this case and you just need to declare that you know this by ignoring the signal: $SIG{PIPE}= 'IGNORE';