Hi there. In recent years, primarily to lighten the load across various domains on a small vServer, we've always used a specific domain that served as a mail server exclusively. The existing email accounts on that server may have been from half a dozen domains, but all of them used the same mail server settings of another domain. However, now and then this caused mail delivery errors with some servers such as AT&T and others.
Since we just purchased a brand new vServer package (Linux with Debian 9) last week, this time around we also opted to purchase a second IP number for that server, in order to utilize that particular IP exclusively for the mail server and email accounts from the domains on that server. By using a dedicated IP number for the email server as well as all of the emails contained in the various domains, we're hoping to eliminate any mail delivery errors once and for all. Problem is, we've never tried using a dedicated IP number for our mail server before and we're a bit stuck, hoping to find some assistance here.
I have a beginning admin who's helping me with this and we have the mail server working, but in Thunderbird for example, the incoming/outgoing mails server settings aren't working with the IP number. When we try using the IP number, we receive Security/Certificate Warnings. Yes, I googled Thunderbird mail settings extensively but could only find a post from 2011 which showed a screenshot with precisely what we're doing ... just having the IP number itself in the fields for incoming/outgoing mail server. This is 2018 though and those settings don't appear to work anymore.
But that's why I'm here, because I'm beginning to suspect that something was entered incorrectly either in the Registrar's DNS settings, the mail server installation of the server setup with Debian 9, and/or the mail server settings within i-MSCP. Would someone please be so kind and point me in the right direction for the Debian 9, i-MSCP, and Thunderbird settings? I would greatly appreciate it. Thank you.