You’ve attached restricted media. See Google’s guide on attachments for file types Gmail blocks or flags.
You don’t have permission to email the recipient. Under GDPR, sending unsolicited marketing email without consent is a compliance risk as well as a spam trigger — see Spamhaus’s overview of GDPR and spam.
Your sender information isn’t accurate. The “From” name and address should clearly and honestly identify who’s sending the email.
You’re missing a physical postal address. Most anti-spam laws (GDPR, CAN-SPAM, PECR) require a real postal address in marketing emails.
You’re using spam-trigger words. Phrases common in scam or hard-sell copy get flagged more readily — see ActiveCampaign’s list of spam words to avoid.
Your subject line doesn’t match your content, or reads like clickbait.
You’re sending a large image with little accompanying text. Image-heavy, text-light emails are a classic spam pattern — keep a healthy text-to-image ratio.
There’s no unsubscribe option. As of February 2024, Gmail requires a clearly visible unsubscribe link in the body of any marketing email, and for bulk senders (5,000+ emails/day to Gmail addresses), a one-click unsubscribe header as well. Unsubscribe requests must be honoured within two days.
You’re sending to addresses that don’t exist. Bounces to invalid addresses damage your sender reputation quickly — clean your list regularly.
Your grammar is poor. Genuine businesses proofread; a lot of spam doesn’t.
