SDB:Why should username, hostname and domainname be written
Version: 1.0 -
SuSE version: all
Kernel version: all
XFree86 version: all
Unfortunately problems are constantly appearing in the network area, because the naming standards for username, hostnane and domainname are not conformed. This is why here are summarized the most important guidelines concerning the small writing.
The username has, as far as the upper and lowercase are concerned, can be rather various. However, some mail exchange protocols exist (e.g. POP3, see RFC 1725), that behave indifferent to the upper and lowercase. Consequently, it is appropriate to use always a lowercase username.
RFC 1178: `Choosing a Name for Your Computer'
A quote from it:
Don't expect case to be preserved.
Upper and lowercase characters look the same to a great deal of internet software, often under the assumption that it is doing you a favor. It may seem appropriate to capitalize a name the same way you might do it in English, but convention dictates that computer names appear all lowercase. (And it saves holding down the shift key.)
Consequently it is very strongly recommended to write the hostname in lowercase, since some protocols, particularly NIS, ignore capital letters.
RFC 2065: `Domain Name System Security Extensions'
A quote from it:
For purposes of DNS security, the canonical form for an RR is the RR with domain names (1) fully expanded (no name compression via pointers), (2) all domain name letters set to lower case, and (3) the original TTL substituted for the current TTL.
obliges as well to a domain name's lowercase writing. Even when numerous operators do not conform these convention, this should be any reason for imitations.