Hello,
Did you get the following error in a bounce message?
554 5.7.1 This message has been blocked because it is from a FortiGuard - AntiSpam black IP address. (connection black ip x.x.x.x)
First, check your mail server for problems and make sure it's not sending spam.
When you are done confirm if your IP address is still listed using
this lookup tool.
Then, if you are still listed, and the problem is fixed, send a delisting request to
removespam@fortinet.com