I have several domains registered, and currently use the mail servers from my host. There are two problems:  Their spam protection is rubbish  My outgoing mails from one domain are not getting to external addresses at the moment (they were fine). I've created a mailbox on PlusNet and I've tried to set up Outlook so it uses this to send, and the current mailbox for receive (I will change this later). Email Address: [me@mydomain] SMTP Server: relay.plus.net Outgoing Server Authentication: Log on using [my PlusNet mailbox username and password] (I can't use same settings as incoming mail server, obviously) SMTP Port: 25 I'm getting a 552 error (message rejected for spam ...). I don't see why it reports this, as I have provided authentication. Is this because I'm using an address on my domain as my return address, or because I'm using a different POP server, or something else? If it's because my return address is on my domain, then the plan is a non-starter and I will have to consider another ISP that allows this.