Before we start...

An email address is composed of a local part and a domain: [local part]@[domain].

For which conditions an email or domain would be flagged as spam?

Contains test

If the local part OR domain is exactly “test”

If the local part OR domain begins with “test”

If the local part contains “+test” anywhere

If the local part has “test” followed by any number of digits, and that’s the end (ex: logantest333@madkudu.com)

If the domain contains “.test” anywhere

Some characters are repeated many times

If any character is repeated at least 4 times consecutively

OR

If any pair of letters is repeated at least 4 times (tetetete@gmail.com)

Numbers exceed letters

If the local part is made up of more than half by digits (1234aa@gmail.com)

If there is at least one more digit than there are letters in the local part

If there are at least 6 numbers in the local part

Local part has no letters

If the local part does not contain any letters

Spammy patterns detected!

If the email is longer than 20 and the top 3 most common characters make up more than 70% of characters

Domain end is domain

If the strings before and after the period in the domain are the same (logan@hello.hello)

Domain or local part contains backlisted word or phrase

If the domain contains any phrase from an in-house list of blacklisted words/phrases

Contains asd or sdf twice

If the email contains the sequence of letters “asd” or “sdf” twice

Looks like spam

contains the phrase “noemail” anywhere in it

Local part or domain length is 1

the local part contains contains one character (a@gmail.com) or domain contains exactly one character (logan@a.com)

Local part has no vowels

If the local part of the string is at least 4 characters long, does not contain any numbers, and does not contain any vowels.

Local part low vowel ratio

If the local part is 5 characters long and there are no vowels in it

If the local part is greater than 5 characters and the fraction of vowels is less than 0.08 (specifically, vowels / letters, not vowels / total number of characters. As in, numbers are not being counted when doing the division)

Domain contains short gibberish

If the domain contains any of the following:

asdef

asdf

If the domain looks exactly like any of the following:

asd.com

sdf.com

fsd.com

dsa.com

Contains absurdity

If the local part contains any of the following:

princessleia

If the local part is exactly:

sda

ads

dsa

nothing

abc

sdf

Not F1000 or personal and has numbers in local

There are two consecutive numbers in the local part.