and any action the user performs on messages in one interface will be reflected when the email is accessed via the other interface. There are significant differences in rendering capabilities for many popular webmail services such as Gmail, Outlook.com and Yahoo! Mail. Due to the varying treatment of HTML tags, such as <style> and <head>, as well as CSS rendering inconsistencies, email marketing companies rely on older web development techniques to send cross-platform mail. This usually means a greater reliance on tables and inline stylesheets. Microsoft Windows applications by default create email messages via MAPI. Several vendors produce tools to provide a MAPI interface to webmail. Privacy concerns Although emails stored unencrypted on any service provider's servers can be read by that service provider, specific concerns have been raised regarding webmail services that automatically analyze the contents of users' emails for the purpose of targeted advertising. At least two such services, Gmail and Yahoo! Mail, give users the option to opt out of targeted advertising. Webmail that is accessed over unsecured HTTP may be readable by a third party who has access to the data transmission, such as over an unsecured Wi-Fi connection. This may be avoided by connecting to the webmail service via HTTPS, which encrypts the connection. Gmail has supported HTTPS since launch and in 2014 began requiring it for all webmail connections. Yahoo! Mail added the option to connect over HTTPS in 2013 and made HTTPS required in 2014. See also Comparison of email clients Comparison of mail servers Comparison of webmail providers Email hosting service Hybrid mail References External links email Email clients