Falsehoods programmers believe about email
In the spirit of falsehoods programmers believe about names and time, here’s some falsehoods about email which are all too common.
- Everyone has an email address
- Everyone has exactly one email address
- An email address never changes
- Whenever an address does change, it’s under that user’s control
- Whenever an address does change, it’s because the user specifically requested it to happen
- Whenever an address does change, the old address will continue to work/exist
- Any one email address refers to only one single person
- Unique strings of characters all map to different addresses
- All email is hosted by a centralized system
- When email is sent to a user at a domain, it is delivered to a server whose address matches that domain
- When email is sent by a user at a domain, it is sent by a server whose address matches that domain
- All email comes from a
- You can filter out email based on the TLD or ccTLD from which it originates
- Having a particular ccTLD means that you prefer to receive communications in that country’s native language (for example,
- Email addresses only contain letters
- Email addresses only contain letters and numbers
- Email addresses only contain letters, numbers, and a handful of common punctuation marks (e.g.
- Email addresses will have at least one letter in them
- An email address like
- Email is a reliable transport
- Email is an instantaneous transport
- Emails will be sent within a few minutes of their scheduling
- Emails will be sent within a few hours of their scheduling
- Emails will be sent within a few days of their scheduling
- Emails will be received soon after they’re sent
- When an email is sent it immediately goes to its destination server
- If an email bounces, the address is invalid
- If an email doesn’t bounce, the address is valid
- An address which is valid will always be valid, and an address which is invalid will always be invalid
- All email is sent via SMTP over TCP/IP port 25
- All email is sent via SMTP over TCP/IP
- All email is sent via SMTP over IP
- All email is sent via SMTP
- All email servers support the various vendor extensions by the current “everyone uses this vendor” vendor (Microsoft, Google, etc.)
- An email can only have one
Date:header on a message is legitimate
Received:headers will always be no earlier than the
- All email clients support HTML attachments
- All email clients support HTML message bodies
- All email clients support MIME encoding
- Email is secure
- Encrypted email is secure
- All email is accessed via webmail
- All email is accessed via webmail or IMAP
- All email is accessed via webmail, IMAP, or POP3
- Nobody uses email anymore
See also: email is bad
Update I’m getting some good additions from folks' responses and I’ll be adding them as I see them.
- Anyone with a .edu address is a student
- Anyone with a .edu address is a student or faculty
- Students and faculty will use their .edu address to sign up for all of their Internet accounts
Additional suggestions from a reddit thread:
- All universities provide an .edu address
- Domains will be handled uniformly between email and HTTP
- Only the owner of an address can send mail from that address
- Email attachment size will be accurate to the storage size of the attachment; relatedly, attachment filenames are the correct filenames for those file types, and that it’s safe to extract attachments to those filenames
- It is valid to remove
+suffixesfrom email addresses (e.g.
- Users actually know their own email address
From Jens Alfke:
- Email addresses are case-sensitive / can be compared by == or strcmp
- A reply to an email sent to address X will come from X (this is the mistake made by things that say “Reply with REMOVE to unsubscribe”)
- If you receive email at address X, you are capable of sending email whose From header is X.
A good one that was posted by many folks when this post went viral but seems to first be by benoliver999 on lobste.rs:
- If you send a url in an email, the user will be the first to click it
Update, 9/1/2022: Wow, I am getting overwhelmed with comments and suggestions. This really struck a nerve, huh!
I don’t think I’ll be adding any more things to this list. But here’s a few threads you can follow and post comments on:
Also, I moderate every single comment that comes to this site, so please be patient if a comment you post doesn’t appear immediately.
Finally, see this followup.
Before commenting, please read the comment policy.
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