Sorry...posted this in wrong thread to start with. Why does O2 force use of O2's smtp server (or relay) for outgoing mail? I gather it's to stop O2 users sending spam, but no other ISP I've checked does the same. One of several consequences is that my visitors have to change their email account settings if they want to send non-web-based email while on my network. I can visit them (they have BT, Virgin, Plusnet and others), and send email from Outlook without changing anything, but not vice versa. A solution is to pay O2 for a static ip address, but the extra £5/month makes O2 look expensive for anyone who doesn't need static ip for other reasons. I'm on 14-days cooling-off with O2 from today and will have to switch away from them if this can't be fixed without hassle or cost.
Thanks guys - port 26 is no good with GMX but 587 is good (all other settings remain the same as for port 25). Port 465 with SSL works too. Port 587 works with 1&1. Gmail advises 587 in the first place, so that's ok. Why on earth couldn't any of the O2 techies (I spoke to at least 4) suggest trying other ports? Now to see if the more-obscure email providers I use are ok with 587. My visitors will still have to edit their email accounts but at least everything seems ok for me.