Guys,

There was an error sending your message: Failed to connect to localhost:25 [SMTP: Failed to connect socket:

I have found its due to csf settings. please set as the following variables,

SMTP_BLOCK = 0
SMTP_ALLOWLOCAL = 1

If SMTP_BLOCK is set to 0, then iptables should not be blocking any localhost connections as the lo: device is whitelisted.