Cannot assign requested address - connect (2)

[fst]

Infos:

• Used Zammad version: 5.0
• Used Zammad installation type: package
• Operating system: Centos 8
• Browser + version: Firefox 78.12.Oesr (64.bit)

Expected behavior:

• Smooth setup of Microsoft email

Actual behavior:

• It fails due to “Cannot assign requested address - connect (2) for (…)”. Please, refer to the figure below
  
  

A snapshot of the production.log right after trying to perform this operation (twice) is given below.

Steps to reproduce the behavior:

• I follow the installation steps, but this step didn’t work.

Thanks.

[MrGeneration]

Are you sure that the IPv6 setup of your host is working as expected?
Does pinging via IPv6 and general IPv6 communication work in both directions?