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Hyperlinks on websites and in documents could be used to open the default e-mail client, and prepare an e-mail for the user. This is called the Mailto Protocol. It could be implemented by filling the “href” attribute of the <a> element with a value starting with “mailto:” and followed by one or more e-mailaddresses.

choose a mail client

What Windows 8 does when you click on a mailto: link

This is useful for triggering the user to send a mail to a specified address. But there is a maximum number of characters for the value of the “href” attribute that the Mailto Protocal can handle. So there is also a limitation to the uses this client side mail mechanism. Avoid too ambitious use, for example sending a large number of e-mailaddresses, the mail subject and a considerable mail body to the mail client. The following character limits apply to the complete contents of the “href” attribute, including the subject and body key-value pairs.

Unfortunately, there is not one single limitation to the Mailto Protocol. Rather, the character limit differs from browser and mail client.

A common combination would be Microsoft Outlook and a browser like Internet Explorer 9, Mozzilla Firefox or Google Chrome. For these combinations a character limit of exactly 2046 applies. The same number applies to combinations of IE9, Firefox or Chrome with Windows Live Mail.

For using Gmail, the maximum number of characters is less exact. I tested extensively with Firefox and Gmail, and I could not exactly pinpoint a number. Around 1620 characters usually worked fine.

The champions would be a combination of Windows 8 Mail and Internet Explorer 10. Or a combination of Apple Mail and Safari. The mail client is able to receive a number of 2083 characters, which is exactly the maximum length of a URL in IE10.