When sending an email to a recipient with Advanced Email Security, sender may receive a bounce back stating ESMTP not accepting connections. The error indicates senders IP address is suspected of sending spam and is blacklisted.
To resolve it perform the steps below:
- Check sender's IP address for being blacklisted in any RBL (Realtime Black List): http://mxtoolbox.com/blacklists.aspx. Ask sender to submit an IP removal request to RBLs.
- Check IP reputation on mail filters: contact Support and provide sender's IP address.