Adding a fake "RE:" or "FWD:" at the start of your subject line is not advisable.
Many email clients and anti-spam systems now flag these tactics as suspicious.

Exclamation marks are often associated with spam or promotional emails.

A well-crafted question engages the reader's curiosity, prompting them to open the email to find the answer or learn more

Fully lowercased subject lines create a casual, personal feel and help emails stand out in the inbox.

Subject lines with all cap words both look like they're shouting and like you are a spammer.

Emojis in subject lines can trigger spam filters, appear unprofessional, and may not display correctly across all platforms.