Apr 30 19:52:43 web postfix/smtp: connect to gmail-smtp-in.l.google.com[2a00:1450:4001:c02::1b]:25: Network is unreachable
seems as if your server tries to connect to google by ipv6 but there is no ipv6 network connection possible.
Try to set:
inet_interfaces = IPV4
in postfix main.cf to force postfix to use ipv4