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No-cap email address, =, all-cap email address, ?.

Do Capitals In Email Addresses Make Any Difference?

          May 29, 2019

Mostly you see email addresses that have no capitals, but you may have seen email addresses that were all caps or mixed caps and small letters. You may have wondered whether you can do this yourself when giving out your own email address, perhaps to emphasize some part of it.

The answer is it shouldn't make any difference, i.e. you can if you want to ... unless there is some bad programming along the way, which there may be given the plague of IT incompetence.

Email addresses consist of a username, which is that of the email server computer account, and a domain name, which is the email server computer's address on the Internet. For example, in the email address dr.duane.thresher@alum.mit.edu, dr.duane.thresher is the username and alum.mit.edu is the domain name. Capitals can make a difference in the username but usually accounts are created with no-caps usernames and then when an incoming email address is checked, by comparison, for whether it has an account there, the incoming email address username is, via programming, automatically made into no-caps before comparison. Domain names are defined as no-caps in the standards, so the same no-caps programming is applied to them.

This is very basic programming, i.e. basic IT competence, but given the plague of IT incompetence, sometimes caps in email addresses cause problems. I myself have had this problem with the U.S. Postal Service (USPS) on their usps.com website; see The U.S. Mail SHOULD Be Worried About Email Competition.

It's safest to just use no caps in email addresses, but I risk it in some situations.