Cannot send message (Email body not accepted due to the following reason 5.7.0 security issue
I think that this is a server issue. Who is your email provider? Can you post the complete message received from your server?
Some servers will not allow executable attachments or certain links in emails. But that depends on the server you are using, and not the email client.
Hi, Not sure, GMail is the eMail provider.
Attaches is the error for your reference.
So that is Google blocking your message. If you go the page mentioned in the error, you can see why it was blocked.