Outgoing smtp blocked

To me more specific, i am trying to use sendgrid.com as a third party smtp service for my custom email marketing software.
It was working fine until we applied further security settings to the configserver firewall installed on the server.
One solution was to whitelist the ip address of sendgrid or smtp.sendgrid.net, but after contacting them, they said the block of ip adresses changes regularly, and no ips could be provided and whitelisted.
I tried adding the following to my /etc/csf/csf.rignore (you can do that via command line or via whm lfd csf.rignore-reverse DNS Lookup)
smtp.sendgrid.net
.sendgrid.net
.smtp.sendgrid.net
then restarted csf and lfd but the smtp was still being blocked!
After checking my configserver security settings SMTP_BLOCK was set to on, so i adjusted the following: SMTP_ALLOWUSER and added the user name that is using this service and it worked fine (must restart lfd and csf)
Note that this is not the safest override for the issue as ideally it would be better to only allow a specific smtp server, this is because allowing the user in the SMTP_ALLOWUSER will allow any script using smtp, under that user, to be executed.
But it did the trick until i find a more secure fix.