To avoid falling into spam, follow our general recommendations:
Do not exceed Gmail's daily limit on email sending (250 emails/day max) or any other provider limits.
Disable the open tracking pixel (in this case you do not receive stats on your open rate, but you get more credibility for not having images in the email body).
Increase the delay between sending emails. We recommend 90-120 seconds for the best performance.
Always include an opt-out link when reaching out to cold contacts.
There is no guarantee that your prospects are not going to mark you as spam unless you make your lead lists more targeted or bring more value to your contacts when emailing them.
For more information, see the article How to avoid falling emails into the Spam.