For security consideration currently all the outgoing email sent from cPanel platform will be filtered by mailchannel. You will receive a bounce back email indicates your email is blocked by mailchannels as below:
Result:TLS_AES_256_GCM_SHA384:256 CV=yes: SMTP error from remote mail server after end of data: 550 5.7.1 [CS] Message blocked. If this is a false positive, please report this to your hosting service provider. See https://console.mailchannels.net/insights/bounce?auid=instrampxe0y3a&sender=xxxxx%40cpanel-563-syd.hostingww.com&txid=16c26c527406c2dd
How do I unblock my email account from mailchannel?
You are able to unblock them by clicking the links provided in the bounce-back email, such as the below example:
When on the mailchannels page, you'll click Not Spam to report the issue -
Please be advised that mailchannel is adaptive and there is no pre-set limit to how much email you can send in a given window of time. However, as a general rule of thumb, it's good to slowly ramp up the rate at which you send emails in order to avoid this message.
As the system notices that you are sending a good email that recipients appear to like receiving, the amount that you can send will gradually increase.