[CentOS] Mail has quit working

Mon Aug 27 11:57:41 UTC 2018
Richard <lists-centos at listmail.innovate.net>

> Date: Monday, August 27, 2018 07:42:48 -0400
> From: TE Dukes <tdukes at palmettoshopper.com>
>> From: CentOS [mailto:centos-bounces at centos.org] On Behalf Of
>> Richard Sent: Monday, August 27, 2018 7:29 AM
>> Since the localhost4 approach worked, commend out the ipv6
>> localhost entries in your /etc/hosts file, then try:
> IP6 is commented out
>>     dig @localhost localhost a
> That works
>> again. If that works try:
>>     telnet localhost 143
> This also works
>> once again. If those work, it would seem that your ipv6 is messed
>> up and your system is trying it first and not falling back to ipv4.
>> Regarding your nameserver list in /etc/resolv.conf. If you have a
>> working nameserver you generally don't include external
>> nameservers in that list. So, if non-ipv6 things seem to work, I'd
>> remove the two non-127 nameservers from that list.
> Removed the two nameservers. Still can't access mail. Getting
> connection to storage server failed on the roundcube login page.

That you can now successfully get to "localhost" is good progress.
Seems you want to stay away from ipv6 networking issues unless/until
you resolve whatever that issue is.

Roundcube is, potentially, a totally separate issue. I don't use it,
so can only suggest minimal debugging ideas.

What is the hostname that you use to get to your roundcube instance?
Can you resolve that:

   dig <hostname> a

If you get an answer, is the ipnumber correct?

Note, if the hostname for your roundcube instance is one of the ipv6
entries in your /etc/hosts file, I'd remove that - and either put in
an ipv4 entry or put an entry for it in your dns.