What is a 'Mail block - general' error?

The recipient’s email server blocks inbound mail from the sender’s server, which may be due to blacklisting. A mail block is recorded when the receiving server blocks an email completely, rejecting the message without any attempt to deliver it to the inbox.
The reasons for this block are:

• Your reply-to address is blacklisted
• One of your sending IPs is temporarily blocked
• One of your sending domains is temporarily blacklisted
• The receiving server only accepts white-listed senders

 
To know more about Email Bounces and Error Codes, click here.