You may find that you are not able to send email from an OVH server. It may be due to outbound network traffic for port 25 is blocked.
You would want to verify your cPanel server is allowing the traffic out on the Exim ports.
Review your firewall rules on the cPanel server and see if the ports are allowed outbound.
# iptables -L -n | egrep 'Chain|25|465|587'
Chain INPUT (policy ACCEPT)
Chain FORWARD (policy ACCEPT)
Chain OUTPUT (policy ACCEPT)
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 multiport dports 25,26,465,587 owner GID match 209
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 multiport dports 25,26,465,587 owner GID match 12
ACCEPT tcp -- 0.0.0.0/0 127.0.0.1 multiport dports 25,26,465,587 owner UID match 201
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 multiport dports 25,26,465,587 owner UID match 0
The above output shows ports 25,26,465,587 are allowed out of the server.
If your server has the ports allowed outbound and the email still is not leaving the server, you may wish to check that the OVH environment is allowing traffic outbound.
Is there a location where changes can be made?
Depending on the hosting environment, there appears to be an OVH Control Panel available that allows you to reach a firewall management page.
OVHcloud Control Panel:
If you have access to it, you may wish to try using this documentation to modify firewall rules in the OVH environment.
If you find yourself unable to access those locations, you may wish to reach out to OVH support.