Group User Mailaccout for example info@xy

I would like to install an info@xy mail adresse which can be opperated with two persons min.

I dont want to just forward (via alias) the info mail to their personal mail adresses because i want, that the see when person A answers for exapmple to the first six mails and then person B just continue with the seven ......

I could solve this unsing:
IMAP accounts hosted on a secondary server, if IMAP would work
Creating an IFO User if shareing of MAilboxes would be supported

How do i can handle this issue