Should domain names and email addresses always be lowercase to make sure you get where you want to go? Or is this completely irrelevant? Google's mail servers, for example, have strange settings with interesting effects, which I will briefly introduce below.
Google, which recently started offering @gmail.com addresses to German users, ignores periods before the spider monkey and the spelling is case-insensitive. The following email addresses are completely equivalent:
- davidvielhuber@gmail.com
- dav.id.v.iel.hu.ber@gmail.com
- DAVIDVIELHUBER@gmail.com
- David.Vielhuber@gmail.com
The standard RFC 2821 specifies how this should normally be handled:
The local-part of a mailbox MUST BE treated as case sensitive. Therefore, SMTP implementations MUST take care to preserve the case of mailbox local-parts. Mailbox domains are not case sensitive. In particular, for some hosts the user "smith" is different from the user "Smith". However, exploiting the case sensitivity of mailbox local-parts impedes interoperability and is discouraged.
This means that the domain name behind the spider monkey is to be treated as case-insensitive and the local part in front of the spider monkey is to be treated as case-sensitive. In the vast majority of cases, however, mail servers are very tolerant. I recommend always lowercase both email addresses and domain names.
A small aside: You can also add an additional address directly in front of the @, which will be ignored during delivery (and can therefore be used, for example, for rule-based filtering of emails):
- davidvielhuber+ganz-wichtig@gmail.com
- davidvielhuber+newsletter@gmail.com
- davidvielhuber+gewinnspiel@gmail.com