The 550 5.7.1 [CS] message indicates that email originating from your account contains a virus.

How can I unblock my account as an end user?

Secure your account against compromise by performing the following:

• Change your password. Ensure your new password has a minimum length of eight characters and uses a mixture of upper and lower case letters, numbers, and special characters.
• Verify that your operating system is running with the latest security updates.
• Update your anti-virus software and conduct a full scan of your system to ensure that a spammer has not installed spam-sending malware on your computer.

If these steps do not resolve the problem, please file a support request with your web hosting provider.  

How can I unblock an end user account as a service provider?

As a first step, verify that the account that is blocked is not compromised and is not sending spam. If the account is compromised, the account has to be secured.

If this is a false positive, please raise a support ticket by writing to support@mailchannels.com with the following details

1) Sender email address

2) Subject

3) Recipient email address

4) Date & Time