by Charles Miller

A friend shared the email address of another friend with me, but when I tried to use it the email I sent bounced back to me as undeliverable. It turned out that the friend who had shared the email address had made a tiny mistake, by omitting the tiniest key on his keyboard… the period.

When my friend shared the email address for John.Doe@yahoo.com he omitted the period between John and Doe. Since my friend used Gmail, he probably thought that was okay because Gmail users are allowed add or remove extra periods from the username part of their own Gmail address at will.

Google ignores periods in the username for delivery purposes, but this is not a universal or industry-wide standard. Yahoo Mail along with most other email providers does follow the industry standards, so periods matter in Yahoo email addresses for proper email delivery.

A more technical way of stating this is to say the Simple Mail Transfer Protocol (SMTP) standards define periods as valid characters in an email address. This means periods are treated as significant characters just as are numbers and the letters of the alphabet. Gmail chose to break the rules and define the period as an invalid character in only the names portion of their email addresses (only before the @ sign and not after). This means you should not disregard any periods in an email address, unless it is an @gmail.com address. The reason it is okay to do this with @gmail.com addresses is because Google simply treats periods in the name part of an address as if the periods were never there.

Some software engineer at Google must have though it was a nice “feature” to be able to add extra periods to usernames and to have the system ignore them. I do certainly understand how the periods make John.Q.Public easier for humans to read than johnqpublic, and it has always been allowed to use uppercase or lowercase letters. And it is true there are some tricks you can do with the extra periods to help control unwanted spam emails. Still, Google ignoring all periods in names creates the kind of problems my friend and I encountered.

On the subject of what is and what is not allowed in email address names, there are rules. These rules are important when you create a new email address for yourself; moreover, it can be helpful to sometimes recognize when an email you have received is from a fake address.

The permissible characters in email address usernames are the letters A-Z, digits 0 through 9 plus some other keyboard characters. Letters may be lowercase or uppercase, it makes no difference. There are quite a few keyboard characters that are prohibited from being used in email addresses. These include diacritics, spaces, colon, semicolon, backslash, single quotes, parentheses, ampersand, and many more; but not to worry because no email provider will allow you to create an email address with prohibited characters. There is actually a way to sneak the prohibited characters into a valid email address, but you are not going to hear how to do that kind of hacking from me!

In addition to the preferred numbers and letters, there are quite a few other keyboard characters that are technically legal to use but probably not a good idea to use due to the increased likelihood of their creating confusion. These include the underscore, hyphen, plus sign, apostrophe, exclamation mark, hash (#), caret (^), tilde (~), and the aforementioned PERIOD.

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Charles Miller is a freelance computer consultant with decades of IT experience and a Texan with a lifetime love for Mexico. The opinions expressed are his own. He may be contacted at 415-101-8528 or email FAQ8 (at) SMAguru.com.

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