Thanks for sharing your experience.
Patches to enable rPi support can be found here: https://bitbucket.org/nifgraup/iredmail
Someone tested iRedMail with Debian ARM platform and Respberry Pi before, and it works. Since not many users use those two platforms, so i didn't commit the patch. But this time, your patch was committed moment ago.
and notes are kept in a wiki: https://bitbucket.org/nifgraup/iredmail/wiki/Home
I try to answer the questions in your wiki below:
Possibly related to a failed installation when swap was not enabled: Dovecot package installation fails because IPv6 is not enabled by default on Raspbian. #listen = *, :: can be changed to Listen = * in /etc/dovecot/dovecot.conf to fix the issue. Or modprobe ipv6 and add ipv6 to /etc/modules. iRedMail does not configure IPv6, perhaps listen = * should be by default (until IPv6 is enabled by default of course)?
iRedMail has a sample config file for Dovecot-2.0.x, it enables IPv4 only, no IPv6. So i guess it's caused by Debian itself, it starts Dovecot service during package installation.
ClamAV takes a lot of memory, to the point that the machine is swapping after a fresh install of iRedMail. It should not be installed, but the menu does not allow skipping Clam.
As clearly explained in iRedMail installation guide, in section "System Requirements", iRedMail requires at least 1GB memory for production use. Because Amavisd + SpamAssassin + ClamAV take lots of memory for content based spam/virus scanning.
But it's easy to fix your issue by disabling ClamAV in Amavisd config file, then stop ClamAV service. Both SpamAssassin and ClamAV are invoked by Amavisd, not running as a daemon service.
Also, i'm not sure items listed in "Before running iRedMail.sh" are required or just optional, i suggest you clearly mark them as "required" and "optional" to make things easier. Less steps leads to more success.