SMTP

Click on the red underlined text to get to the source

... Internet and the Internet SMTP transport defined by RFC 821^std10(-> 2821^prop). As the format has seen wider use, ...

... binary data. Such data cannot be transmitted over some transfer protocols. For example, RFC 821^std10(-> 2821^prop) (SMTP) restricts mail messages to 7bit US-ASCII ...

... character sets, while such encodings are clearly required for 7bit SMTP.) ...

... output string. These characters, identified in Table 1, below, are selected so as to be universally representable, and the set excludes characters with particular significance to SMTP (e.g., ".", CR, LF) ...