What is the effect of blacklisting an SMTP server?

When an SMTP server is blacklisted, it means that its IP address or domain has been identified as a source of spam or malicious activity. This action restricts the server's ability to communicate with certain domains or IP addresses, effectively preventing it from successfully sending emails to those locations. Blacklisting serves as a protective measure for email recipients, helping to filter out unwanted or harmful emails from known problematic sources.

As a result, the correct response highlights the primary impact of blacklisting, which is the hindrance it places on the server’s ability to deliver emails, thereby enforcing stricter control over email communications in the network. The other options do not accurately reflect the consequences of blacklisting: it does not improve a server's reputation, does not enhance its email sending capabilities, nor does it relate to encryption standards.