thanks_in_advance's questions

I have set up an email server using docker-mailserver.

DKIM, SPF, and DMARC are configured fine.

SSL was set up using Let's Encrypt. Server has TLS and STARTTLS enabled.

I ran a TLS/SSL test on https://www.checktls.com/TestReceiver , and it said that my SSL works fine:

I am able to use Mozilla Thunderbird to receive and send email via the server:

However, when logging in to Thunderbird to receive email via IMAP, or when sending via SMTP, I see this warning (I am still able to send and receive email if I click on the "Confirm Security Exception" button.)

I checked a couple of other email TLS/SSL testing sites (1 and 2) and they seem to think my certs are not set up correctly ("The certificate doesn't match hostname").

Thoughts?

Update: I've managed to reach the point where imap.domainname.com is recognized by Thunderbird to have a valid certificate, but not imap.domainname.com:143. What would be a fix for this please?

I was playing around with a DigitalOcean droplet. Linux Ubuntu 18.04.

I had a root password about 8 alphanumeric characters long. Port 22. It would take about 3 days for hackers with Chinese IP addresses to break into it.

I replicated this experiment a couple of times. And each time it took about 3 days.

So I stopped using a password and switched to SSH keys.

DigitalOcean generates an initial root password that's 26 alphanumeric characters long. Is that much more secure? (After the first log-in DigitalOcean requires you to choose your own password, so I would choose shorter passwords of 8 characters so I could memorize them.)

Your thoughts on how long would it take hackers to brute force it?

I have a single Digital Ocean droplet with 5 websites hosted on it via virtualhost. Everything works fine. Their domain names point to each one individually. Using Ubuntu 14.04 and Apache.

I want to add a sixth "test" site, without a domain name pointing to it. I want to use it to test out some WordPress stuff. The physical location of the home page to this site is:

/var/www/test_site/html/index.html

Let's say my server's IP address is 198.51.100.55

What do I need to do to make this home page available to anyone on the internet as follows?

http://198.51.100.55/test_site/html/index.html

I wanted www.domain1.tld/domain2 to point to /www/directory2

So I added an 'Alias line' to my Virtualhost config apache2/sites-available/domain1.conf like this:

<VirtualHost *:80>  
    ServerName www.domain1.tld
    DocumentRoot /www/directory1

    Alias /domain2 /www/directory2    #Alias line
</VirtualHost>

Now I've removed that 'Alias line' and added a new Virtualhost config apache2/sites-available/domain2.conf where www.domain2.tld points to /www/directory2.

However, when I visit www.domain2.tld via a browser, the URL changes to www.domain1.tld/domain2 and I get a page saying "Not Found, The requested URL /domain2 was not found on this server"

How do I undo whatever the 'Alias line' did? It seems to have permanently modified some hosts - type file in my server.

(In case it matters, all this was in the service of a PrestaShop installation.)