Unconfirmed errors

When I SEND (forward/reply-to) an email, quite often an error message appears that says : “[SMTP] An attempt to connect to (my email address) failed. This could be caused by temporary server unavailability or incorrect settings.” I get the option to ignore, and when I do that, the email appears to be sent normally and another error window opens says ‘There are no errors’. How can I avoid this annoyance ?