If the subject line of your message reads like a subject line commonly used in spam messages then your list members (or their email filters) will likely confuse it with spam and possibly file complaints or block your future emails.
To improve the chances of your message getting opened AND to reduce the chances of someone filing a spam complaint against you, ask yourself these questions when composing your message's subject line:
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Consider using your list name and a similar subject line each time you send a message. For example, many organizations use this format as their message's subject line:
Weekly Newsletter: newsletter's topic for that issue, the date.
If a list member sees something recognizable about you in the subject line, you will likely see an increased open rate while simultaneously reducing or eliminating spam complaints.
In addition, using personalization tactics such as first name mail merge tags (e.g.: <firstname>) in email subject lines is often confused with spam. Spammers started using this method of personalizing subject lines several years ago in order to mislead email recipients to open the emails. The method was overused and email users began to associate any such email as spam.