This site browses the 4927 emails from Really Good Emails to count the use of certain HTML and CSS features. The numbers on this page indicate the percentage of HTML emails that use the corresponding HTML or CSS feature at least once.
Data is updated every month.

Doctypes Percentage
<!doctype html>
 69.33225%
<!doctype html public "-//w3c//dtd xhtml 1.0 transitional//en" "http://www.w3.org/tr/xhtml1/dtd/xhtml1-transitional.dtd">
 16.54151%
<!doctype html public "-//w3c//dtd xhtml 1.0 strict//en" "http://www.w3.org/tr/xhtml1/dtd/xhtml1-strict.dtd">
 2.98356%
<!doctype html public "-//w3c//dtd html 4.01 transitional//en" "http://www.w3.org/tr/html4/loose.dtd">
 1.94845%
<!doctype html public "-//w3c//dtd html 4.01//en" "http://www.w3.org/tr/html4/strict.dtd">
 0.73067%
<!doctype html public "-//w3c//dtd html 4.0 transitional//en" "http://www.w3.org/tr/rec-html40/loose.dtd">
 0.48711%
<!doctype>
 0.28415%
<!doctype html public "-//w3c//dtd html 4.01 transitional//en">
 0.24356%
<!doctype html public "-//w3c//dtd xhtml 1.0 transitional//en" "https://www.w3.org/tr/xhtml1/dtd/xhtml1-transitional.dtd">
 0.22326%
<!doctype html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office">
 0.06089%
<!doctype html public " -//w3c//dtd html 4.01 transitional//en" "http://www.w3.org/tr/html4/loose.dtd">
 0.04059%
<!doctype html public "-//w3c//dtd html 3.2//en">
 0.04059%
<!doctype html public "-//w3c//dtd xhtml 1.0 transitional//en">
 0.04059%
<!doctype html "-//w3c//dtd xhtml 1.0 transitional//en" "http://www.w3.org/tr/xhtml1/dtd/xhtml1-transitional.dtd">
 0.04059%
<!doctype html public "-//w3c//dtd xhtml 1.0 transitional" "https://www.w3.org/tr/xhtml1/dtd/xhtml1-transitional.dtd">
 0.0203%
<!doctype html public "--//w3c//dtd xhtml 1.0 transitional//en" "http://www.w3.org/tr/xhtml1/dtd/xhtml1-transitional.dtd">
 0.0203%
<!doctype html public"-//w3c//dtd xhtml 1.0 transitional//en""http://www.w3.org/tr/xhtml1/dtd/xhtml1-transitional.dtd">
 0.0203%
<!doctype html public "-//w3c//dtd html 4.01 transitional =//en">
 0.0203%
<!doctype html public "-//w3c//dtd html 4.01 transitional//en" "https://www.w3.org/tr/html4/loose.dtd">
 0.0203%
<!doctype html public "-//w3c//dtd xhtml 1.0 transitional//en""http://www.w3.org/tr/xhtml1/dtd/xhtml1-transitional.dtd">
 0.0203%
<!doctype html public "-//w3c//dtd xhtml 1.0 strict//en" "https://www.w3.org/tr/xhtml1/dtd/xhtml1-strict.dtd">
 0.0203%
<!doctype html public "-//w3c//dtd xhtml 1.0 transitional//en" "http://www.w3.org/tr/xhtml1/dtd/xhtml1-transitional.dtd" xmlns="http://www.w3.org/1999/xhtml" xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlsn:o="urn:schemas-microsoft-com:office:office">
 0.0203%
<!doctype html public"-//w3c//dtd xhtml 1.0 transitional//en" "http://www.w3.org/tr/xhtml1/dtd/xhtml1-transitional.dtd">
 0.0203%
<!doctype html public "-//w3c//dtd xhtml 1.0 strict//en" "http://www.w3.org/tr/xhtml1/dtd/xhtml1-transitional.dtd">
 0.0203%