No, if you have received the blacklist notification, you are not blocked from sending mail. You can continue to mail while you work through the remediation steps.
The only time we will ever block you from sending mail is if you trigger a listing at Spamhaus, the world’s most respected and widely used blacklist. If this happens, you will receive a call or email to let you know what’s going on and we will work with you to resolve the issue. This is a rare occurrence.
Additional Resources:
Can you give me the spam trap address that triggered the listing?
What is a spamtrap, or spam trap, and why does it matter?
What is a blacklist?
How does Marketo respond to blacklisting and spam notifications?
Top blacklists - What you need to know
Blacklist Remediation
Successful Reconfirmation
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