Mailook - Identify & fix your email deliverability issues for free 👀
Mailivery - Reach the Inbox, not the spam folder.
PromoTab - This tiny tool uses a real Gmail account to check if your emails will land in the Primary inbox of a reader or if it's stuck in the promotions tab or SPAM folder.
Postal - Open source mail delivery platform, alternative to Mailgun or Sendgrid
Mailjet - All-in-one email service provider that provides maximum insight and deliverability results for both marketing and transactional emails.
WP Email Delivery - Managed email delivery for WordPress