I don't use Spamex. But looking at their website and FAQ, I don't see any mention of allowing customers to use their SMTP. It's only an online browser-based service when you send messages.
If you try to use a SMTP server which is not controlled by the Spamex company to send messages from your email client using a spamex.com From address, you will have difficulties.
- Many (probably most) major services don't allow their SMTP server to be used to send messages with a From domain different from the main domain(s) of the service. In other words, if you have a Gmail account, that service doesn't allow you to send messages with a yahoo.com From address. This is to reduce spam.
- If you find and use a SMTP in such a manner (with the From address domain not matching the server IP addresses specified by the From domain owner), most email systems will classify the message as spam.
- This spam reducing behavior has developed over the past decade. Before spammers ruined things for everyone, you could send an email with any From domain through any SMTP server and nobody cared. But not now.
Bill