How long should SQL email fields be?
To best align with RFC 5321 and optimize for practical use, opt for VARCHAR(254) for SQL email fields.
Following the 255-character standard ensures compliance with the Simple Mail Transfer Protocol (SMTP), and efficiently accommodates most real-world email addresses.
Understanding Standards and Practical Application
Analyzing email length in the wild
On average, email lengths gravitate towards 20 characters. It can be observed from a distribution graph that lengths over 40 characters become less frequent. Designing your email field to be VARCHAR(40) allows you to cater to a majority of users without wasting resources.
Normalizing for efficiency
To optimize queries, consider splitting your email field into separate local and domain columns. This conforms to the respective 64 and 255-character constraints and could increase query performance.
Wrestling with the outliers
Every now and then, exceptionally long emails will appear. To accommodate the longest legally possible email, implement VARCHAR(320), but these emails are the exception, not the rule.
Visualization
Visualize an email as a letter (📧) and the SQL email field as a mailbox (📬). How big should the mailbox be?
| Mailbox Type | Can Hold |
|---|---|
| Tiny Mailbox (50) | 📧...📧 (Bursting at the seams) |
| Standard Mailbox (254) | 📧...📧📧 (Just like Home Sweet Home 🏡) |
| Warehouse (512) | 📧📧📧...📧📧 (Anyone lost a 🐱 in here?) |
The Standard Mailbox (254) is the Goldilocks fit for all email sizes. Stick to the standards and your "mail" will always reach its destination!
User-centered Design Considerations
Alignment with UI/UX and Security
Practical field limits improve user experience and can help prevent user errors. Have you tried typing a 250-character email in a form field recently? Yep, not fun! As a bonus, you're protected from evil-doers attempting field-length exploits.
Email Casing
Remember to lowercase the domain of email addresses as domains are case-insensitive. But keep your hands off the local part — some systems are case-sensitive.
Visual Email Verification (VERP)
When generating auto-reply emails, apply VERP to efficiently handle any bounce-backs. This won't affect the field length directly, but it’s a step towards world-class email field management.
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