Package: Debian GNU/Linux Installation Guide
Version: 4.0 for i386
The heading for section 8.5.2 reads "Sending E-Mails Outside The System".
This is incorrect English, with regard to e-mail. "e-mail" (whether hyphenated, or not) is both singular *and* plural. Thus, I can write "I sent email to John" (meaning one message); or "I sent email to John" (meaning two-or-more messages).
In order to avoid confusion, or the appearance of incorrect usage, we recommend that people/publications follow this format:
Single message: Sending E-Mail Outside The System
Multiple messages: Sending E-Mail Messages Outside the System
The second format is preferable, since a single message is a subset of multiple messages.