Email subject is the first things the recipient read when viewing your message. An eye-catching subject line can raise the recipient’s attention and greatly improve the open rate. A email subject shout short, descriptive, and encourage the reader to open and read your message.
Not to use the word “free”
As “free” is often considered to be a spam keyword. Most email servers filter emails that contain spam keywords in their subject line and the emails are most likely to be marked as JUNK/SPAM.
Don’t just write Newsletter #1, #2, #3
If you email your newsletters to customer, don’t just write subject line as “Newsletter #1″ or “Newsletter #2″. The open rate will gradually drop as it doesn’t encourage the recipient to open it.
You should provide a descriptive subject lines instead. For example, you can pick the title of the main article in your newsletter as subject.
Don’t use capitals or exclamation marks
It should not be in all capital letters, or contain exclamation marks.
Keep it short
Try and keep to around 50 characters including spaces. Most popular email readers don’t display more characters than this.