How long should SQL email fields be? [duplicate]

Question

This question already has an answer here:

• What is the optimal length for an email address in a database? 8 answers

I recognize that an email address can basically be indefinitely long so any size I impose on my varchar email address field is going to be arbitrary. However, I was wondering what the "standard" is? How long do you guys make it? (same question for Name field...)

update: Apparently the max length for an email address is 320 (<=64 name part, <= 255 domain). Do you use this?

Answer 1

For email, regardless of the spec, I virtually always go with 512 (nvarchar). Names and surnames are similar.

Really, you need to look at how much you care about having a little extra data. For me, mostly, it's not a worry, so I'll err on the conservative side. But if you've decided, through logically and accurate means, that you'll need to conserve space, then do so. But in general, be conservative with field sizes, and life shall be good.

Note that probably not all email clients support the RFC, so regardless of what it says, you may encounter different things in the wild.

Answer 2

RFC 5321 (the current SMTP spec, obsoletes RFC2821) states:

4.5.3.1.1. Local-part

The maximum total length of a user name or other local-part is 64
octets.

4.5.3.1.2. Domain

The maximum total length of a domain name or number is 255 octets.

This pertains to just localpart@domain, for a total of 320 ASCII (7-bit) characters.

If you plan to normalize your data, perhaps by splitting the localpart and domain into separate fields, additional things to keep in mind:

• A technique known as VERP may result in full-length localparts for automatically generated mail (may not be relevant to your use case)
• domains are case insensitive; recommend lowercasing the domain portion
• localparts are case sensitive; [e-mail] and [e-mail] are technically different addresses per the specs, although the policy at the domain.com may be to treat the two addresses as equivalent. It's best to restrict localpart case folding to domains that are known to do this.

Answer 3

I've in the past just done 255 because that's the so-ingrained standard of short but not too short input. That, and I'm a creature of habit.

However, since the max is 319, I'd do nvarchar(320) on the column. Gotta remember the @!

nvarchar won't use the space that you don't need, so if you only have a 20 character email address, it will only take up 20 bytes. This is in contrast to a nchar which will always take up its maximum (it right-pads the value with spaces).

I'd also use nvarchar in lieu of varchar since it's Unicode. Given the volatility of email addresses, this is definitely the way to go.

Answer 4

If you're really being pendantic about it, make a username varchar(60), domain varchar(255). Then you can do ridiculous statistics on domain usage that is slightly faster than doing it as a single field. If you're feeling really gun-ho about optimization, that will also make your SMTP server able to send out emails with fewer connections / better batching.

Answer 5

I use varchar(64) i do not think anyone could have longer email

Answer 6

The theoretical limit is really long but do you really need worry about these long Email addresses? If someone can't login with a 100-char Email, do you really care? We actually prefer they can't.

Some statistical data may shed some light on the issue. We analyzed a database with over 10 million Email addresses. These addresses are not confirmed so there are invalid ones. Here are some interesting facts,

1. The longest valid one is 89.
2. There are hundreds longer ones up to the limit of our column (255) but they are apparently fake by visual inspection.
3. The peak of the length distribution is at 19.
4. There isn't long tail. Everything falls off sharply after 38.

We cleaned up the DB by throwing away anything longer than 40. The good news is that no one has complained but the bad news is not many records got cleaned out.