Darn. I did check the get-evarchive, not the set-evarchivepermission (12.3).
I have not tried using EVPM to set permission on SMTP archives, but below pwershell script can create the .ini file for evpm from a csv. (not my script, a colleague figured this out)
Create CSV file with Archivename, Account to create ini file for evpm. You need to add the default lines for evpm (directory/site), but the ini file will work. I used this for adding new domain accounts to existing archives. You might be able to replace ($item.ADACount) by the actual account (Domain\Account), but that requires testing. When the inifile is created, use 3 easily checked archives for your testrun.
Import-Module ImportExcel
$items = Import-CSV "d:\input_Permission.CSV"
$ini = ""
ForEach ($item in $items) {
$ini += "[ArchivePermissions]`r`n"
$ini += "ArchiveName = $($item.Aname)`r`n"
$ini += "GrantAcess = read write delete, $($item.ADACount)`r`n"
$ini += "`r`n"}
$ini | Out-File "H:\output_Permission.ini" -Encoding unicode