I have recently started receiving and error when I try to forward or send all messages. They are incorrectly identified as spam, phishing or malware, however they are perfectly normal messages and I can see no apparent reasons for this error. I have attached a screenshot which gives a typical example. Any help from the community to resolve this will be appreciated. 
There are some instances where mail servers reject messages because of the signature. If you are using a signature in eM Client, can you disable it and then try again.
Otherwise, I think this error is coming from your email provider. Maybe you could contact them and ask for some input. You may find a more detailed error in the Log tab.
Gary, thanks for your response. I’m not using a signature so that suggests it’s caused by the email provider. I will follow up with them.
Certainly looks like it might be. Will be interesting to hear what they say.