To resolve Barracuda blocklist issues and improve email deliverability, several email marketing best practices should be followed. These include maintaining a good sender reputation through email authentication (SPF, DKIM, DMARC), consistently providing valuable content, and actively managing your email lists by segmenting them, removing unengaged subscribers (sunset policy), and validating email addresses. Proactive monitoring of IP and domain reputation, warming up IP addresses gradually, and setting up feedback loops with ISPs are also crucial. If blocklisted, identify and rectify the cause, then contact Barracuda support with proof of resolution to request delisting.