HTML Email is the use of a subset of HTML to provide formatting and semantic markup capabilities in emails that are not available with plain text: Text can be linked without displaying URLs, or breaking long URLs into sections. The text is wrapped to fit the width of the display window, rather than uniformly breaking each line in 78 characters (defined in RFC 5322, as required in the old text terminal). This allows the inclusion of pictures, tables, and mathematical diagrams or formulas in-line as images, which are difficult to convey (usually using ASCII art).
Video HTML email
Adoption
Most graphics email clients support HTML email, and many defaults to it. Many of these clients include GUI editors to compose HTML emails and rendering engines to display received HTML email.
Since its conception, some people have rejected all HTML email (and even MIME itself), for various reasons. For example, the ASCII Ribbon Campaign recommends that all emails should be sent in ASCII text format. The campaign was unsuccessful and abandoned in 2013. Though still considered inappropriate in many newsgroup posts and mailing lists, adoption for personal and business letters only increases over time. Some of those who strongly oppose it when they first come out now see it as the most innocuous.
According to surveys by online marketing companies, adoption of HTML-enabled email clients is now almost universal, with less than 3% reporting that they use text-only clients. Most users prefer to receive HTML email through plain text.
Maps HTML email
Compatibility
Email software that complies with RFC 2822 is only required to support plain text, not HTML format. Sending HTML-formatted email can cause problems if the recipient's email client does not support it. In the worst case, the recipient will see the HTML code instead of the intended message.
Among email clients that support HTML, some do not make it consistent with W3C specifications, and many inappropriate HTML emails, which can cause rendering or shipping issues, especially for Gmail users.
Specifically, the & lt; head & gt; , which is used to place CSS style rules for all HTML documents, is not well supported, is sometimes completely stripped, causing the in-line style declaration to be de facto standard, even though the in-line style declaration inefficient and unsuccessful use of HTML capabilities to separate styles from the content. Although a settlement has been developed, this does not cause frustration among developers of the bulletin, spawned the Grassroots Email Standard Project, which values ​​email clients about acid-test rendering, inspired by Web Standards projects, and lobbies developers to improve their products. To persuade Google to increase rendering in Gmail, for example, they publish montage of web developers web grimacing, which results in the attention of an employee.
Style
Some senders may rely heavily on large, colorful, or annoying fonts, making messages more difficult to read. For those who feel annoyed with this formatting, some user agents allow the reader to partially override the formatting (for example, Mozilla Thunderbird allows specifying minimum font size); However, this capability is not available globally. Further, differences in the optical display between the sender and the reader can help distinguish the author from each part, increasing readability.
Multi-part format
Many email servers are configured to automatically generate versions of plain text messages and send them along with HTML versions, to ensure that they can be read even by text-only email clients, using Content-Type: multipart/alternative , as specified in RFC 1521. The message itself is of the type text/plain type, read by the text-only client, and the second with text/html , which is read by HTML-enabled clients. Simple text versions may lose important formatting information, however. (For example, a mathematical equation may lose superscripts and take on an entirely new meaning.)
Many mailing lists are blocking HTML emails by accident, either deleting the HTML section until leaving a plain text section or rejecting the entire message.
The order of the parts is significant. RFC1341 states that: Generally, the user agent that forms the multipart/alternate entity should place the body parts in increasing the order of preference, ie with the last preferred format. For multi-page emails with html and plain-text versions, which means listing the usual text-first and later versions of html, otherwise the client can by default display the plain text version even if the html version is available.
Message size
HTML email is bigger than plain text. Even if no special formatting is used, there will be additional cost of the tags used in minimal HTML documents, and if formatting is very often used, it may be much higher. Multi-part messages, with duplicate copies of the same content in different formats, zoom in further in size. The plain text section of multi-part messages can be retrieved by itself, though, using the IMAP FETCH command.
Although the difference in download time between plain text and mixed messages (which could be a factor of ten or more) was of concern in the 1990s (when most users accessed email servers via slow modems), on modern connections the difference is negligible for most people, especially when compared to images, music files, or other common attachments.
Security vulnerabilities
HTML allows links to show up as arbitrary text, so instead of displaying full URLs, links may show only partial or easy-to-use target names. This can be used in phishing attacks, where users are fooled into believing that links point to authoritative source websites (such as banks), visit them, and inadvertently reveal personal details (such as bank account numbers) to scammers.
If an email contains web bugs (inline content from an external server, such as an image), the server can remind the third party that the email has been opened. This is a potential privacy risk, revealing that the email address is real (so it can be targeted in the future) and revealed when the message is read. For this reason, some email clients do not load external images until requested by the user.
HTML content requires an email program to use the machine to parse, render and display documents. This can lead to more security vulnerabilities, denial of service or lower performance on older computers.
During periods of increasing network threats, the US Department of Defense converts all incoming HTML emails to text emails.
Multi-part types are meant to show the same content in different ways, but these are sometimes misused; some spam emails use formats to trick spam filters into believing that messages are legitimate. They do this by entering harmless content in the text message section and putting spam in the HTML section (what is shown to users).
Most spam emails are sent in HTML for this reason, so spam filters sometimes give higher spam scores to HTML messages.
See also
- Enriched text - systems like HTML for email using MIME
References
Source of the article : Wikipedia
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