Does anyone have expertise on whether there are any regulations on proper storage of government data? Does anyone know how an agency like the IRS would store their company email and if their claim is a feasible possibility?
I do have direct and extensive experience with government email systems. Caveat, mostly with other agencies but a pretty wide variety of them. Post 9/11 there were broad government initiatives to ensure systems like this were definitely backed up, backups stored offsite and usually along with some type of COOP initiative on top of all that. Maybe the IRS did not participate in that initiative, but I highly doubt it.
That they "lost" this data is highly unlikely in my book.
Yes, retention of records is mandatory due to the Federal Records Act. The IRS should store their e-mail on the server, and use IMAP, MS Exchange, or similar. Failure to properly store records is illegal, and not using a proper mailserver configuration is extremely convenient incompetence. It's so convenient, and so high a degree of incompetence, that it looks very much like willful destruction of evidence.
Records and retention is a large part of my current project. It permeates even the lowest levels, and it's practically impossible for the narrative to occur. I say practically impossible, because there is always some way some idiot can screw up big enough that this happens, but this narrative didn't happen. I'd stake 3 digits on it.