What is the optimal length for an email address in a database?
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.
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):
Just use varchar(50). Longer emails are crap, every time.
Just look how long 50 chars is:
peoplewithanemail@ddressthislongjustuseashorterone
If you allow 255 character emails:
- Displaying them can mess up your UI (at best they will be cut off, at worst they push your containers and margins around) and
- Malicious users can do things with them you can't anticipate (like those cases where hackers used a free online API to store a bunch of data)
(Statistics show that no-one actually enters more than about 50 chars for a legit email address, see e.g.: pageman's answer https://stackoverflow.com/a/1199245/87861)