In case you occur problems with sending emails through smtp.simply.com we suggest you ensure the following:
That you've actually entered exactly "smtp.simply.com" at the outgoing server, and that the hostname is spelled correctly.
If you use port 25 to send out, then try to use 587, 2525 or 8080 instead.
Ensure that you've ticked in the column "Server to outgoing server requires permission". This can usually be found under "Advanced account settings" in your mail client.
Ensure that you use the same login information to the outgoing server as you do on the incoming. And ensure that the information is spelt correctly on the incoming server as well.
Ensure that antivirus and firewall programs are not blocking the connection. Eventually, disable these in order to see if it fixes the issue.