As HTML mail is more complex than plain text, it is also more prone to compatibility and consistency problems. According to surveys by [[online marketing]] companies, the vast majority of Internet users can access HTML mail, and a smaller majoritynumber, preferthough itstill overthe plain textmajority, butprefer it mayover notplain render consistently across platforms and softwaretext.<ref name="emaillabs statistics">[http://www.emaillabs.com/resources/resources_statistics.html Email Marketing Statistics and Metrics]</ref><ref name="clickz data">[http://www.clickz.com/showPage.html?page=1428551 Real-World Email Client Usage: The Hard Data]</ref> As HTML mail is more complex than plain text, however, it is also more prone to compatibility issues and problems with rendering consistently across platforms and software.
NoteMany HTML-based GUI [[email client]]s automatically convert common plain text characters, like '''-''' and '''"''', into their proper typographic equivalents, like '''—''' and '''“''', which are not part of 7-bit [[ASCII]]. This can cause translation problems in other users' clients.{{citation needed}} that [[Unicode]] supports many such complex characters, but font support issues with Unicode limit the usefulness of this possibility.
Many HTML-based GUI [[email client]]s automatically convert common plain text characters, like '''-''' and '''"''', into their proper typographic equivalents, like '''—''' and '''“''', which are not part of 7-bit [[ASCII]]. This can cause translation problems in other users' clients.{{citation needed}}
Some popular email clients do not render consistently with W3C specifications, and many HTML emails are not compliant, either, which may cause rendering or delivery problems, especially for users of MSN or Hotmail.<ref name="emaillabs statistics">[http://www.emaillabs.com/resources/resources_statistics.html Email Marketing Statistics and Metrics]</ref>
