What is the optimal length for an email address in a database?

user_54964 0
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Here is an extracted portion of my query, reflecting the EMAIL_ADDRESS column data type and property:

EMAIL_ADDRESS CHARACTER VARYING(20) NOT NULL,

However, John Saunders uses VARYING(256).

This suggests me that I have not necessarily understood the VARYING correctly.

I understand it such that the length of an email address is 20 characters in my case, while 256 for Jodn.

Context in John's code

CREATE TABLE so."User"
  (
    USER_ID SERIAL NOT NULL,
    USER_NAME CHARACTER VARYING(50) NOT NULL,
    EMAIL_ADDRESS CHARACTER VARYING(256) NOT NULL, // Here
    HASHED_PASSWORD so.HashedPassword NOT NULL,
    OPEN_ID CHARACTER VARYING(512),                                                         
    A_MODERATOR BOOLEAN,
    LOGGED_IN BOOLEAN,
    HAS_BEEN_SENT_A_MODERATOR_MESSAGE BOOLEAN,
    CONSTRAINT User_PK PRIMARY KEY(USER_ID)
  );

I have never seen email addresses longer than 20 characters, used by ordinary people.

What is the optimal length for an email address in a database?

database-design email database performance
9 Answers

The maximum length of an email address is 254 characters.

Every email address is composed of two parts. The local part that comes before the '@' sign, and the domain part that follows it. In "user@example.com", the local part is "user", and the domain part is "example.com".

The local part must not exceed 64 characters and the domain part cannot be longer than 255 characters.

The combined length of the local + @ + domain parts of an email address must not exceed 254 characters. As described in RFC3696 Errata ID 1690.

I got the original part of this information from here

user_953990

from Ask Metafilter:

My data comes from a database of 323 addresses. The distribution has some upper-end outliers (positively-skewed). It is normally distributed without the outliers (I tested it.)

Min: 12 1st quartile: 19 Mean (w/ outliers): 23.04 Mean w/o outliers): 22.79 3rd quartile: 26 Max (w/ outliers): 47 Max (w/o outliers): 35

Median: 23 Mode: 24 Std. Dev (w/ outliers): 5.20 Std. Dev (w/o outliers): 4.70

Ranges based on data including outliers 68.2% of data 17.8 - 28.2 95.4% of data 12.6 - 33.4 99.7% of data 7.4 - 38.6

Ranges based on data outliers excluded 68.2% of data 18.1 - 27.5 95.4% of data 13.4 - 32.2 99.7% of data 8.7 - 36.9

If you sign up for http://www.abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijk.com/ then your email address would surely be an outlier :)

Here's What is the maximum safe length of an email address to allow in a website form? on Raycon with a slightly different mean (N=50,496, mean=23):

Email address length distribution

user_642530

My work email address is more than 20 characters!

Read the appropriate RFC specification:

"The local-part of an e-mail address may be up to 64 characters long and the domain name may have a maximum of 255 characters"

user_1403920

Variable character types in databases don't occupy unneeded space. Thus, there is no reason to constrain such fields as much as possible. Depending on the name of a person, the naming scheme used by their organization and their domain name, an address can easily exceed 20 characters.

There is no limit as to the length of local-part and domain-name in RFC-2822. RFC-2181 limits the domain name to 255 octets/characters though.

Again, since a varchar only uses the space actually used by the string you store, there is no reason to have a small limit for email address length. Just go with 512 and stop worrying. Everything else is premature optimization

Lars_O_234240

A CHAR(20) field will always take up 20 characters, whether you use it all or not. (Often padded with spaces at the end.) A VARCHAR(20) field will take up up to 20 characters, but may take up less. One benefit of CHAR()s constant width is fast jumping to a row in a table, because you can just calculate the index it must be on. The drawback is wasting space.

The benefit of constant-sized CHAR(x)'s is lost if you have any VARCHAR(x) columns in your table. I seem to recall that MySQL silently converted any CHAR() fields into VARCHAR() behind the scenes if some columns were VARCHAR()s.

Admin1

TLDR Answer

Use a VARCHAR(256) to store the 256 character maximum entailed in current, prevailing RFC Internet standards.

Source

SMTP originally defined what a path was in RFC821, published August 1982, which is an official Internet Standard (most RFC's are only proposals). To quote it...

...a reverse-path, specifies who the mail is from.

...a forward-path, which specifies who the mail is to.

RFC2821, published in April 2001, is the Obsoleted Standard that defined our present maximum values for local-parts, domains, and paths. A new Draft Standard, RFC5321, published in October 2008, keeps the same limits. To quote RFC2821...

4.5.3.1.3. Path

The maximum total length of a reverse-path or forward-path is 256 characters (including the punctuation and element separators).

Common Mistaken Answers

In February 2004, RFC3696 was published and it mistakenly cites the max limit of email addresses as 320 characters. But this was an "informational-only" document, which states...

"This memo provides information for the Internet community. It does not specify an Internet standard of any kind."

We can disregard this limit, then, as it is published before RFC5321, which is a Draft Internet Standard that keeps the email address max limit unchanged at 256 characters.

user_24305490

As others have said, way bigger than 20. 256 + 64 sounds good to me, and is RFC compliant.

The only reason to not have such a large value for your database is if you are worrying about performance or space, and if you are doing that then I'm 99.99999999999999% sure that is premature optimization.

Go big.

user_29610
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