5.2.18 Common Address Formatting Errors: RFC-822 Section 6.1

Errors in formatting or parsing 822 addresses are unfortunately common. This section mentions only the most common errors. A User Agent MUST accept all valid RFC-822 address formats, and MUST NOT generate illegal address syntax.

• A common error is to leave out the semicolon after a group identifier.

• Some systems fail to fully-qualify domain names in messages they generate. The right-hand side of an "@" sign in a header address field MUST be a fully-qualified domain name.

  For example, some systems fail to fully-qualify the From: address; this prevents a "reply" command in the user interface from automatically constructing a return address.

  DISCUSSION:

  Although RFC-822 allows the local use of abbreviated domain names within a domain, the application of RFC-822 in Internet mail does not allow this. The intent is that an Internet host must not send an SMTP message header containing an abbreviated domain name in an address field. This allows the address fields of the header to be passed without alteration across the Internet, as required in Section 5.2.6.

• Some systems mis-parse multiple-hop explicit source routes such as:

      @relay1,@relay2,@relay3:user@domain.
  

• Some systems over-qualify domain names by adding a trailing dot to some or all domain names in addresses or message-ids. This violates RFC-822 syntax.