I've had my server running fine for the last month or so since migrating from a previous Debian install. All email accounts worked fine on my laptop (thunderbird) and my phone. As of yesterday, Gmail on my phone no longer receives or sends emails. Everything on my laptop still works. I have not made any changes at all apart from fixing an the password recovery which wasn't set up properly (https://www.howtoforge.com/community/threads/password-reset-feature-not-working.87415/) I don't know if this is a knock-on effect that's now causing email not to work on my phone. I deleted an account on my phone and tried to set it up again, and it fails. It takes a long time attempting "Validating server settings" then comes up with an "Email security not guaranteed" message. The strange thing is I have it set up for STARTTLS, using a valid certificate (issued by LE). I've tried adding the account in MS Outlook also installed on my laptop and that's fine - no errors. My guess is something has changed, a security protocol has been enabled or disabled that Gmail doesn't like, maybe as a result of setting up the password reset system / sending system emails in ISPconfig. But I can't figure out how to get any further debugging on the phone. Any ideas?
yes, using the FQDN - mail1.xavserver.co.uk I wondered whether the settings for system emails should be localhost instead of the FQDN, but gathered that wouldn't work with SSL as the certificate name wouldn't match. In either case, I've always used the FQDN for gmail app and it's always worked. I've also tried accepting all certificates in case that was the case, but no difference. Still says "Couldn't open connection to server."
Finally got to the bottom of the problem. It was an IPv6 issue. First found out that if I turned off WiFi and used 4G, it worked fine. Then went digging further and a combination of my ISP and local router and also rDNS wasn't configured on my server properly for IPv6... Long story short, it's all ok now
