I have a client that is a dial-up user of an ISP. She has a website hosted elsewhere. She has a POP3 email account with that website. I have her email software setup to send and receive using the mail.herdomain.com server name. However, sometimes her emails do not get sent. I really don't think this is an issue of the hosting server.
I called the ISP tech support to see if they are blocking port 25, and essentially they are (although I don't think it is real blocking because sometimes her emails do go through). The tech support at the ISP said that in order to send email without being thought of as a spammer was to put mail.isp.com as the sending email server.
This confuses me because I would think that sending email from one domain on a different domain email server would be considered spam more than trying to send the email from the correct server.
I hope I've made this clear enough...I'm just looking for someone to explain it.
This is a small local ISP (Anent.com/megapipe). I've asked the client to change their outgoing mail server like the ISP asked, but I haven't heard back from the client to know if it works. And, in talking with the ISP tech support, I'm sure they will not be adding DNS entries to help us (unfortunately, the client lives way out, and this ISP is about the only choice).