Symptoms
3rd-party testing sites report issues with the SMTP Transaction Time on your server.
Description
Automated tools establish a standard SMTP connection to the server and note the time it takes. On cPanel servers, the "Introduce a delay into the SMTP transaction for unknown hosts and messages detected as spam" option in "Exim Configuration Manager" is enabled by default. This option helps prevent spam from being delivered to your server.
A user sending spam is likely using automated tools to send as many messages as possible in a short period. However, a legitimate mail server sending an email will have no issue waiting the extra seconds to connect and send the message. Automated online tools encounter the same problem as spammers, as they often don't wait the full 15 seconds allowed for the transaction to occur.
Workaround
The problems reported by the 3rd-party testing sites are false positives and can be ignored.