What is the subject line in HTML?

Question

A host company sent this Client Template, containing some directions. But I didn't understand this paragraph:

To avoid being flagged as spam, do not using the following elements in the subject line: &, ?, !, capital letters, repetitions of the same word, numbers, percentage marks at the beginning or the end of the title.

Answer 1

HTML没有主题行，但电子邮件却有主题行，这可能意味着如果您的网站发送了任何内容，则需要遵循这些准则，以避免将其标记为垃圾邮件。